TY - JOUR
A1 - Mazarei, Elham
A1 - Penschke, Christopher
A1 - Saalfrank, Peter
T1 - Band gap engineering in two-dimensional materials by functionalization
BT - Methylation of graphene and graphene bilayers
JF - ACS Omega
N2 - Graphene is well-knownfor its unique combination of electricaland mechanical properties. However, its vanishing band gap limitsthe use of graphene in microelectronics. Covalent functionalizationof graphene has been a common approach to address this critical issueand introduce a band gap. In this Article, we systematically analyzethe functionalization of single-layer graphene (SLG) and bilayer graphene(BLG) with methyl (CH3) using periodic density functionaltheory (DFT) at the PBE+D3 level of theory. We also include a comparisonof methylated single-layer and bilayer graphene, as well as a discussionof different methylation options (radicalic, cationic, and anionic).For SLG, methyl coverages ranging from 1/8 to 1/1, (i.e.,the fully methylated analogue of graphane) are considered. We findthat up to a coverage theta of 1/2, graphene readily accepts CH3, with neighbor CH3 groups preferring trans positions. Above theta = 1/2, the tendency to accept further CH3 weakens and the lattice constant increases. The band gapbehaves less regularly, but overall it increases with increasing methylcoverage. Thus, methylated graphene shows potential for developingband gap-tuned microelectronics devices and may offer further functionalizationoptions. To guide in the interpretation of methylation experiments,vibrational signatures of various species are characterized by normal-modeanalysis (NMA), their vibrational density of states (VDOS), and infrared(IR) spectra, the latter two are obtained from ab initio moleculardynamics (AIMD) in combination with a velocity-velocity autocorrelationfunction (VVAF) approach.
KW - Adsorption
KW - Alkyls
KW - Band structure
KW - Electrical conductivity
KW - Two dimensional materials
Y1 - 2023
U6 - https://doi.org/10.1021/acsomega.3c02068
SN - 2470-1343
VL - 8
IS - 24
SP - 22026
EP - 22041
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Mayer, Dennis
A1 - Lever, Fabiano
A1 - Picconi, David
A1 - Metje, Jan
A1 - Ališauskas, Skirmantas
A1 - Calegari, Francesca
A1 - Düsterer, Stefan
A1 - Ehlert, Christopher
A1 - Feifel, Raimund
A1 - Niebuhr, Mario
A1 - Manschwetus, Bastian
A1 - Kuhlmann, Marion
A1 - Mazza, Tommaso
A1 - Robinson, Matthew Scott
A1 - Squibb, Richard J.
A1 - Trabattoni, Andrea
A1 - Wallner, Måns
A1 - Saalfrank, Peter
A1 - Wolf, Thomas J. A.
A1 - Gühr, Markus
T1 - Following excited-state chemical shifts in molecular ultrafast x-ray photoelectron spectroscopy
JF - Nature communications
N2 - Imaging the charge flow in photoexcited molecules would provide key information on photophysical and photochemical processes. Here the authors demonstrate tracking in real time after photoexcitation the change in charge density at a specific site of 2-thiouracil using time-resolved X-ray photoelectron spectroscopy. The conversion of photon energy into other energetic forms in molecules is accompanied by charge moving on ultrafast timescales. We directly observe the charge motion at a specific site in an electronically excited molecule using time-resolved x-ray photoelectron spectroscopy (TR-XPS). We extend the concept of static chemical shift from conventional XPS by the excited-state chemical shift (ESCS), which is connected to the charge in the framework of a potential model. This allows us to invert TR-XPS spectra to the dynamic charge at a specific atom. We demonstrate the power of TR-XPS by using sulphur 2p-core-electron-emission probing to study the UV-excited dynamics of 2-thiouracil. The method allows us to discover that a major part of the population relaxes to the molecular ground state within 220-250 fs. In addition, a 250-fs oscillation, visible in the kinetic energy of the TR-XPS, reveals a coherent exchange of population among electronic states.
Y1 - 2022
U6 - https://doi.org/10.1038/s41467-021-27908-y
SN - 2041-1723
N1 - Publisher correction: https://doi.org/10.1038/s41467-022-28584-2
VL - 13
IS - 1
PB - Nature Research
CY - Berlin
ER -
TY - JOUR
A1 - Melani, Giacomo
A1 - Nagata, Yuki
A1 - Saalfrank, Peter
T1 - Vibrational energy relaxation of interfacial OH on a water-covered alpha-Al2O3(0001) surface
BT - a non-equilibrium ab initio molecular dynamics study
JF - Physical chemistry, chemical physics : PCCP ; a journal of European chemical societies
N2 - Vibrational relaxation of adsorbates is a sensitive tool to probe energy transfer at gas/solid and liquid/solid interfaces. The most direct way to study relaxation dynamics uses time-resolved spectroscopy. Here we report on a non-equilibrium ab initio molecular dynamics (NE-AIMD) methodology to model vibrational relaxation of OH vibrations on a hydroxylated, water-covered alpha-Al2O3(0001) surface. In our NE-AIMD approach, after exciting selected O-H bonds their coupling to surface phonons and to the water adlayer is analyzed in detail, by following both the energy flow in time, as well as the time-evolution of Vibrational Density of States (VDOS) curves. The latter are obtained from Time-dependent Correlation Functions (TCFs) and serve as prototypical, generic representatives of time-resolved vibrational spectra. As most important results, (i) we find a few-picosecond lifetime of the excited modes and (ii) identify both hydrogen-bonded aluminols and water molecules in the adsorbed water layer as main dissipative channels, while the direct coupling to Al2O3 surface phonons is of minor importance on the timescales of interest. Our NE-AIMD/TCF methodology is powerful for complex adsorbate systems, in principle even reacting ones, and opens a way towards time-resolved vibrational spectroscopy.
Y1 - 2021
U6 - https://doi.org/10.1039/d0cp03777j
SN - 1463-9076
SN - 1463-9084
VL - 23
IS - 13
SP - 7714
EP - 7723
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Kuntze, Kim
A1 - Viljakka, Jani
A1 - Titov, Evgenii
A1 - Ahmed, Zafar
A1 - Kalenius, Elina
A1 - Saalfrank, Peter
A1 - Priimagi, Arri
T1 - Towards low-energy-light-driven bistable photoswitches
BT - ortho-fluoroaminoazobenzenes
JF - Photochemical & photobiological sciences / European Society for Photobiology
N2 - Thermally stable photoswitches that are driven with low-energy light are rare, yet crucial for extending the applicability of photoresponsive molecules and materials towards, e.g., living systems. Combined ortho-fluorination and -amination couples high visible light absorptivity of o-aminoazobenzenes with the extraordinary bistability of o-fluoroazobenzenes. Herein, we report a library of easily accessible o-aminofluoroazobenzenes and establish structure-property relationships regarding spectral qualities, visible light isomerization efficiency and thermal stability of the cis-isomer with respect to the degree of o-substitution and choice of amino substituent. We rationalize the experimental results with quantum chemical calculations, revealing the nature of low-lying excited states and providing insight into thermal isomerization. The synthesized azobenzenes absorb at up to 600 nm and their thermal cis-lifetimes range from milliseconds to months. The most unique example can be driven from trans to cis with any wavelength from UV up to 595 nm, while still exhibiting a thermal cis-lifetime of 81 days.
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Y1 - 2022
U6 - https://doi.org/10.1007/s43630-021-00145-4
SN - 1474-905X
SN - 1474-9092
VL - 21
IS - 2
SP - 159
EP - 173
PB - Springer
CY - Heidelberg
ER -
TY - JOUR
A1 - Yue, Yanhua
A1 - Melani, Giacomo
A1 - Kirsch, Harald
A1 - Paarmann, Alexander
A1 - Saalfrank, Peter
A1 - Campen, Richard Kramer
A1 - Tong, Yujin
T1 - Structure and Reactivity of a-Al2O3(0001) Surfaces: How Do Al-I and Gibbsite-like Terminations Interconvert?
JF - The journal of physical chemistry / publ. weekly by the American Chemical Society. C, Energy, materials, and catalysis
N2 - The alpha-Al2O3(0001) surface has been extensively studied because of its significance in both fundamental research and application. Prior work suggests that in ultra-high-vacuum (UHV), in the absence of water, the so-called Al-I termination is thermodynamically favored, while in ambient, in contact with liquid water, a Gibbsite-like layer is created. While the view of the alpha- Al2O3(0001)/H2O(l) interface appears relatively clear in theory, experimental characterization of this system has resulted in estimates of surface acidity, i.e., isoelectric points, that differ by 4 pH units and surface structure that in some reports has non-hydrogen-bonded surface aluminol (Al-OH) groups and in others does not. In this study, we employed vibrational sum frequency spectroscopy (VSFS) and density functional theory (DFT) simulation to study the surface phonon modes of the differently terminated alpha-Al2O3(0001) surfaces in both UHV and ambient. We find that, on either water dosing of the Al-I in UHV or heat-induced dehydroxylation of the Gibbsite-like in ambient, the surfaces do not interconvert. This observation offers a new explanation for disagreements in prior work on the alpha-Al2O3(0001)/liquid water interface -different preparation methods may create surfaces that do not interconvert-and shows that the surface phonon spectral response offers a novel probe of interfacial hydrogen bonding structure.
Y1 - 2022
U6 - https://doi.org/10.1021/acs.jpcc.2c03743
SN - 1932-7447
SN - 1932-7455
VL - 126
IS - 31
SP - 13467
EP - 13476
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Mullan, Thomas
A1 - Maschio, Lorenzo
A1 - Saalfrank, Peter
A1 - Usvyat, Denis
T1 - Reaction barriers on non-conducting surfaces beyond periodic local MP2
BT - Diffusion of hydrogen on alpha-Al2O3 (0001) as a test case
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2 - The quest for "chemical accuracy" is becoming more and more demanded in the field of structure and kinetics of molecules at solid surfaces. In this paper, as an example, we focus on the barrier for hydrogen diffusion on a alpha-Al2O3 (0001) surface, aiming for a couple cluster singles, doubles, and perturbative triples [CCSD(T)]-level benchmark. We employ the density functional theory (DFT) optimized minimum and transition state structures reported by Heiden, Usvyat, and Saalfrank [J. Phys. Chem. C 123, 6675 (2019)]. The barrier is first evaluated at the periodic Hartree-Fock and local Moller-Plesset second-order perturbation (MP2) level of theory. The possible sources of errors are then analyzed, which includes basis set incompleteness error, frozen core, density fitting, local approximation errors, as well as the MP2 method error. Using periodic and embedded fragment models, corrections to these errors are evaluated. In particular, two corrections are found to be non-negligible (both from the chemical accuracy perspective and at the scale of the barrier value of 0.72 eV): the correction to the frozen core-approximation of 0.06 eV and the CCSD(T) correction of 0.07 eV. Our correlated wave function results are compared to barriers obtained from DFT. Among the tested DFT functionals, the best performing for this barrier is B3LYP-D3.
Y1 - 2022
U6 - https://doi.org/10.1063/5.0082805
SN - 0021-9606
SN - 1089-7690
VL - 156
IS - 7
PB - AIP Publishing
CY - Melville
ER -
TY - JOUR
A1 - Yang, Jin
A1 - Ghosh, Samrat
A1 - Roeser, Jérôme
A1 - Acharjya, Amitava
A1 - Penschke, Christopher
A1 - Tsutsui, Yusuke
A1 - Rabeah, Jabor
A1 - Wang, Tianyi
A1 - Tameu, Simon Yves Djoko
A1 - Ye, Meng-Yang
A1 - Grüneberg, Julia
A1 - Li, Shuang
A1 - Li, Changxia
A1 - Schomaecker, Reinhard
A1 - Van de Krol, Roel
A1 - Seki, Shu
A1 - Saalfrank, Peter
A1 - Thomas, Arne
T1 - Constitutional isomerism of the linkages in donor–acceptor covalent organic frameworks and its impact on photocatalysis
JF - Nature Communications
N2 - When new covalent organic frameworks (COFs) are designed, the main efforts are typically focused on selecting specific building blocks with certain geometries and properties to control the structure and function of the final COFs. The nature of the linkage (imine, boroxine, vinyl, etc.) between these building blocks naturally also defines their properties. However, besides the linkage type, the orientation, i.e., the constitutional isomerism of these linkages, has rarely been considered so far as an essential aspect. In this work, three pairs of constitutionally isomeric imine-linked donor-acceptor (D-A) COFs are synthesized, which are different in the orientation of the imine bonds (D-C=N-A (DCNA) and D-N=C-A (DNCA)). The constitutional isomers show substantial differences in their photophysical properties and consequently in their photocatalytic performance. Indeed, all DCNA COFs show enhanced photocatalytic H2 evolution performance than the corresponding DNCA COFs. Besides the imine COFs shown here, it can be concluded that the proposed concept of constitutional isomerism of linkages in COFs is quite universal and should be considered when designing and tuning the properties of COFs.
Y1 - 2022
U6 - https://doi.org/10.1038/s41467-022-33875-9
SN - 2041-1723
VL - 13
IS - 1
PB - Nature Publishing Group UK
CY - [London]
ER -
TY - JOUR
A1 - Bouakline, Foudhil
A1 - Saalfrank, Peter
T1 - Seemingly asymmetric atom-localized electronic densities following laser-dissociation of homonuclear diatomics
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistry
N2 - Recent experiments on laser-dissociation of aligned homonuclear diatomic molecules show an asymmetric forward-backward (spatial) electron-localization along the laser polarization axis. Most theoretical models attribute this asymmetry to interference effects between gerade and ungerade vibronic states. Presumably due to alignment, these models neglect molecular rotations and hence infer an asymmetric (post-dissociation) charge distribution over the two identical nuclei. In this paper, we question the equivalence that is made between spatial electron-localization, observed in experiments, and atomic electron-localization, alluded by these theoretical models. We show that (seeming) agreement between these models and experiments is due to an unfortunate omission of nuclear permutation symmetry, i.e., quantum statistics. Enforcement of the latter requires mandatory inclusion of the molecular rotational degree of freedom, even for perfectly aligned molecules. Unlike previous interpretations, we ascribe spatial electron-localization to the laser creation of a rovibronic wavepacket that involves field-free molecular eigenstates with opposite space-inversion symmetry i.e., even and odd parity. Space-inversion symmetry breaking would then lead to an asymmetric distribution of the (space-fixed) electronic density over the forward and backward hemisphere. However, owing to the simultaneous coexistence of two indistinguishable molecular orientational isomers, our analytical and computational results show that the post-dissociation electronic density along a specified space-fixed axis is equally shared between the two identical nuclei-a result that is in perfect accordance with the principle of the indistinguishability of identical particles. Published under an exclusive license by AIP Publishing.
Y1 - 2021
U6 - https://doi.org/10.1063/5.0049710
SN - 0021-9606
SN - 1089-7690
VL - 154
IS - 23
PB - American Institute of Physics
CY - Melville
ER -
TY - JOUR
A1 - Schürmann, Robin
A1 - Titov, Evgenii
A1 - Ebel, Kenny
A1 - Kogikoski Junior, Sergio
A1 - Mostafa, Amr
A1 - Saalfrank, Peter
A1 - Milosavljević, Aleksandar R.
A1 - Bald, Ilko
T1 - The electronic structure of the metal-organic interface of isolated ligand coated gold nanoparticles
JF - Nanoscale Advances
N2 - Light induced electron transfer reactions of molecules on the surface of noble metal nanoparticles (NPs) depend significantly on the electronic properties of the metal-organic interface. Hybridized metal-molecule states and dipoles at the interface alter the work function and facilitate or hinder electron transfer between the NPs and ligand. X-ray photoelectron spectroscopy (XPS) measurements of isolated AuNPs coated with thiolated ligands in a vacuum have been performed as a function of photon energy, and the depth dependent information of the metal-organic interface has been obtained. The role of surface dipoles in the XPS measurements of isolated ligand coated NPs is discussed and the binding energy of the Au 4f states is shifted by around 0.8 eV in the outer atomic layers of 4-nitrothiophenol coated AuNPs, facilitating electron transport towards the molecules. Moreover, the influence of the interface dipole depends significantly on the adsorbed ligand molecules. The present study paves the way towards the engineering of the electronic properties of the nanoparticle surface, which is of utmost importance for the application of plasmonic nanoparticles in the fields of heterogeneous catalysis and solar energy conversion.
Y1 - 2022
U6 - https://doi.org/10.1039/d1na00737h
SN - 2516-0230
VL - 4
IS - 6
SP - 1599
EP - 1607
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Fischer, Eric Wolfgang
A1 - Werther, Michael
A1 - Bouakline, Foudhil
A1 - Grossmann, Frank
A1 - Saalfrank, Peter
T1 - Non-Markovian vibrational relaxation dynamics at surfaces
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2 - Vibrational dynamics of adsorbates near surfaces plays both an important role for applied surface science and as a model lab for studying fundamental problems of open quantum systems. We employ a previously developed model for the relaxation of a D-Si-Si bending mode at a D:Si(100)-(2 x 1) surface, induced by a "bath " of more than 2000 phonon modes [Lorenz and P. Saalfrank, Chem. Phys. 482, 69 (2017)], to extend previous work along various directions. First, we use a Hierarchical Effective Mode (HEM) model [Fischer et al., J. Chem. Phys. 153, 064704 (2020)] to study relaxation of higher excited vibrational states than hitherto done by solving a high-dimensional system-bath time-dependent Schrodinger equation (TDSE). In the HEM approach, (many) real bath modes are replaced by (much less) effective bath modes. Accordingly, we are able to examine scaling laws for vibrational relaxation lifetimes for a realistic surface science problem. Second, we compare the performance of the multilayer multiconfigurational time-dependent Hartree (ML-MCTDH) approach with that of the recently developed coherent-state-based multi-Davydov-D2 Ansatz [Zhou et al., J. Chem. Phys. 143, 014113 (2015)]. Both approaches work well, with some computational advantages for the latter in the presented context. Third, we apply open-system density matrix theory in comparison with basically "exact " solutions of the multi-mode TDSEs. Specifically, we use an open-system Liouville-von Neumann (LvN) equation treating vibration-phonon coupling as Markovian dissipation in Lindblad form to quantify effects beyond the Born-Markov approximation. Published under an exclusive license by AIP Publishing.
KW - phonons
KW - Vibrational states
KW - Chemical dynamics
KW - Adsorption
KW - Surface science
KW - Open quantum systems
KW - Density-matrix
KW - Coherent states
KW - Markov processes
Y1 - 2022
U6 - https://doi.org/10.1063/5.0092836
SN - 0021-9606
SN - 1089-7690
SN - 1520-9032
VL - 156
IS - 21
PB - AIP Publishing
CY - Melville
ER -
TY - JOUR
A1 - Fischer, Eric Wolfgang
A1 - Anders, Janet
A1 - Saalfrank, Peter
T1 - Cavity-altered thermal isomerization rates and dynamical resonant localization in vibro-polaritonic chemistry
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2 - It has been experimentally demonstrated that reaction rates for molecules embedded in microfluidic optical cavities are altered when compared to rates observed under "ordinary" reaction conditions. However, precise mechanisms of how strong coupling of an optical cavity mode to molecular vibrations affects the reactivity and how resonance behavior emerges are still under dispute. In the present work, we approach these mechanistic issues from the perspective of a thermal model reaction, the inversion of ammonia along the umbrella mode, in the presence of a single-cavity mode of varying frequency and coupling strength. A topological analysis of the related cavity Born-Oppenheimer potential energy surface in combination with quantum mechanical and transition state theory rate calculations reveals two quantum effects, leading to decelerated reaction rates in qualitative agreement with experiments: the stiffening of quantized modes perpendicular to the reaction path at the transition state, which reduces the number of thermally accessible reaction channels, and the broadening of the barrier region, which attenuates tunneling. We find these two effects to be very robust in a fluctuating environment, causing statistical variations of potential parameters, such as the barrier height. Furthermore, by solving the time-dependent Schrodinger equation in the vibrational strong coupling regime, we identify a resonance behavior, in qualitative agreement with experimental and earlier theoretical work. The latter manifests as reduced reaction probability when the cavity frequency omega(c) is tuned resonant to a molecular reactant frequency. We find this effect to be based on the dynamical localization of the vibro-polaritonic wavepacket in the reactant well.
Y1 - 2022
U6 - https://doi.org/10.1063/5.0076434
SN - 0021-9606
SN - 1089-7690
VL - 156
IS - 15
PB - American Institute of Physics
CY - Melville, NY
ER -
TY - JOUR
A1 - Reifarth, Martin
A1 - Bekir, Marek
A1 - Bapolisi, Alain M.
A1 - Titov, Evgenii
A1 - Nusshardt, Fabian
A1 - Nowaczyk, Julius
A1 - Grigoriev, Dmitry
A1 - Sharma, Anjali
A1 - Saalfrank, Peter
A1 - Santer, Svetlana
A1 - Hartlieb, Matthias
A1 - Böker, Alexander
T1 - A dual pH- and light-responsive spiropyrane-based surfactant
BT - investigations on Its switching behavior and remote control over emulsion stability
JF - Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition
N2 - A cationic surfactant containing a spiropyrane unit is prepared exhibiting a dual-responsive adjustability of its surface-active characteristics. The switching mechanism of the system relies on the reversible conversion of the non-ionic spiropyrane (SP) to a zwitterionic merocyanine (MC) and can be controlled by adjusting the pH value and via light, resulting in a pH-dependent photoactivity: While the compound possesses a pronounced difference in surface activity between both forms under acidic conditions, this behavior is suppressed at a neutral pH level. The underlying switching processes are investigated in detail, and a thermodynamic explanation based on a combination of theoretical and experimental results is provided. This complex stimuli-responsive behavior enables remote-control of colloidal systems. To demonstrate its applicability, the surfactant is utilized for the pH-dependent manipulation of oil-in-water emulsions.
KW - Dual-Responsiveness
KW - Manipulation of Emulsion Stability
KW - Spiropyrane
KW - Surfactant
KW - Switchable Surfactants
KW - pH-Dependent Photoresponsivity
Y1 - 2022
U6 - https://doi.org/10.1002/anie.202114687
SN - 1433-7851
SN - 1521-3773
VL - 61
IS - 21
PB - Wiley-VCH
CY - Weinheim
ER -
TY - CHAP
A1 - Saalfrank, Peter
A1 - Bedurke, Florian
A1 - Heide, Chiara
A1 - Klamroth, Tillmann
A1 - Klinkusch, Stefan
A1 - Krause, Pascal
A1 - Nest, Mathias
A1 - Tremblay, Jean Christophe
ED - Ruud, Kenneth
ED - Brändas, Erkki J.
T1 - Molecular attochemistry: correlated electron dynamics driven by light
T2 - Advances in quantum chemistry
N2 - Modern laser technology and ultrafast spectroscopies have pushed the timescales for detecting and manipulating dynamical processes in molecules from the picosecond over femtosecond domains, to the attosecond regime (1 as = 10(-18) s). This way, real-time dynamics of electrons after their photoexcitation can be probed and manipulated. In particular, experiments are moving more and more from atomic and solid state systems to molecules, opening the fields of "molecular electron dynamics" and "attosecond chemistry." Also on the theory side, powerful quantum dynamical tools have been developed to rationalize experiments on ultrafast electron dynamics in molecular species.
In this contribution, we concentrate on theoretical aspects of ultrafast electron dynamics in molecules, mostly driven by lasers. The dynamics will be described with the help of wavefunction-based ab initio methods such as time-dependent configuration interaction (TD-CI) or the multiconfigurational time-dependent Hartree-Fock (MCTDHF) methods. Besides a survey of the methods and their extensions toward, e.g., treatment of ionization, laser pulse optimization, and open quantum systems, two specific examples of applications will be considered: The creation and/or dynamical fate of electronic wavepackets, and the nonlinear optical response to laser pulse excitation in molecules by high harmonic generation (HHG).
KW - dipole approximation
KW - electron dynamics
KW - electronic wavepackets
KW - high harmonic generation
KW - ionization
KW - optimal control theory
KW - time-dependent Schrödinger equation
Y1 - 2020
SN - 978-0-12-819757-8
U6 - https://doi.org/10.1016/bs.aiq.2020.03.001
SN - 0065-3276
VL - 81
SP - 15
EP - 50
PB - Elsevier
CY - Amsterdam [u.a.]
ER -
TY - JOUR
A1 - Tetenoire, Auguste
A1 - Ehlert, Christopher
A1 - Juaristi, Joseba Iñaki
A1 - Saalfrank, Peter
A1 - Alducin, Maite
T1 - Why ultrafast photoinduced CO desorption dominates over oxidation on Ru(0001)
JF - The journal of physical chemistry letters
N2 - CO oxidation on Ru(0001) is a long-standing example of a reaction that, being thermally forbidden in ultrahigh vacuum, can be activated by femtosecond laser pulses. In spite of its relevance, the precise dynamics of the photoinduced oxidation process as well as the reasons behind the dominant role of the competing CO photodesorption remain unclear. Here we use ab initio molecular dynamics with electronic friction that account for the highly excited and nonequilibrated system created by the laser to investigate both reactions. Our simulations successfully reproduce the main experimental findings: the existence of photoinduced oxidation and desorption, the large desorption to oxidation branching ratio, and the changes in the O K-edge X-ray absorption spectra attributed to the initial stage of the oxidation process. Now, we are able to monitor in detail the ultrafast CO desorption and CO oxidation occurring in the highly excited system and to disentangle what causes the unexpected inertness to the otherwise energetically favored oxidation.
Y1 - 2022
U6 - https://doi.org/10.1021/acs.jpclett.2c02327
SN - 1948-7185
VL - 13
IS - 36
SP - 8516
EP - 8521
PB - American Chemical Society
CY - Washington, DC
ER -
TY - JOUR
A1 - Choudhury, Arnab
A1 - DeVine, Jessalyn A. A.
A1 - Sinha, Shreya
A1 - Lau, Jascha Alexander
A1 - Kandratsenka, Alexander
A1 - Schwarzer, Dirk
A1 - Saalfrank, Peter
A1 - Wodtke, Alec Michael
T1 - Condensed-phase isomerization through tunnelling gateways
JF - Nature : the international weekly journal of science
N2 - Quantum mechanical tunnelling describes transmission of matter waves through a barrier with height larger than the energy of the wave(1). Tunnelling becomes important when the de Broglie wavelength of the particle exceeds the barrier thickness; because wavelength increases with decreasing mass, lighter particles tunnel more efficiently than heavier ones. However, there exist examples in condensed-phase chemistry where increasing mass leads to increased tunnelling rates(2). In contrast to the textbook approach, which considers transitions between continuum states, condensed-phase reactions involve transitions between bound states of reactants and products. Here this conceptual distinction is highlighted by experimental measurements of isotopologue-specific tunnelling rates for CO rotational isomerization at an NaCl surface(3,4), showing nonmonotonic mass dependence. A quantum rate theory of isomerization is developed wherein transitions between sub-barrier reactant and product states occur through interaction with the environment. Tunnelling is fastest for specific pairs of states (gateways), the quantum mechanical details of which lead to enhanced cross-barrier coupling; the energies of these gateways arise nonsystematically, giving an erratic mass dependence. Gateways also accelerate ground-state isomerization, acting as leaky holes through the reaction barrier. This simple model provides a way to account for tunnelling in condensed-phase chemistry, and indicates that heavy-atom tunnelling may be more important than typically assumed.
Y1 - 2022
U6 - https://doi.org/10.1038/s41586-022-05451-0
SN - 0028-0836
SN - 1476-4687
VL - 612
IS - 7941
SP - 691
EP - 695
PB - Macmillan Publishers Limited, part of Springer Nature
CY - London
ER -
TY - JOUR
A1 - Kogikoski Junior, Sergio
A1 - Tapio, Kosti
A1 - Edler von Zander, Robert
A1 - Saalfrank, Peter
A1 - Bald, Ilko
T1 - Raman enhancement of nanoparticle dimers self-assembled using DNA origami nanotriangles
JF - Molecules : a journal of synthetic chemistry and natural product chemistry / Molecular Diversity Preservation International
N2 - Surface-enhanced Raman scattering is a powerful approach to detect molecules at very low concentrations, even up to the single-molecule level. One important aspect of the materials used in such a technique is how much the signal is intensified, quantified by the enhancement factor (EF). Herein we obtained the EFs for gold nanoparticle dimers of 60 and 80 nm diameter, respectively, self-assembled using DNA origami nanotriangles. Cy5 and TAMRA were used as surface-enhanced Raman scattering (SERS) probes, which enable the observation of individual nanoparticles and dimers. EF distributions are determined at four distinct wavelengths based on the measurements of around 1000 individual dimer structures. The obtained results show that the EFs for the dimeric assemblies follow a log-normal distribution and are in the range of 10(6) at 633 nm and that the contribution of the molecular resonance effect to the EF is around 2, also showing that the plasmonic resonance is the main source of the observed signal. To support our studies, FDTD simulations of the nanoparticle's electromagnetic field enhancement has been carried out, as well as calculations of the resonance Raman spectra of the dyes using DFT. We observe a very close agreement between the experimental EF distribution and the simulated values.
KW - surface-enhanced Raman scattering
KW - DNA origami
KW - resonance Raman
KW - scattering
KW - nanoparticle dimers
Y1 - 2021
U6 - https://doi.org/10.3390/molecules26061684
SN - 1420-3049
VL - 26
IS - 6
PB - MDPI
CY - Basel
ER -
TY - JOUR
A1 - Witzorky, Christoph
A1 - Paramonov, Guennaddi
A1 - Bouakline, Foudhil
A1 - Jaquet, Ralph
A1 - Saalfrank, Peter
A1 - Klamroth, Tillmann
T1 - Gaussian-type orbital calculations for high harmonic generation in vibrating molecules
BT - Benchmarks for H-2(+)
JF - Journal of chemical theory and computation
N2 - The response of the hydrogen molecular ion, H-2(+), to few-cycle laser pulses of different intensities is simulated. To treat the coupled electron-nuclear motion, we use adiabatic potentials computed with Gaussian-type basis sets together with a heuristic ionization model for the electron and a grid representation for the nuclei. Using this mixed-basis approach, the time-dependent Schrodinger equation is solved, either within the Born-Oppenheimer approximation or with nonadiabatic couplings included. The dipole response spectra are compared to all-grid-based solutions for the three-body problem, which we take as a reference to benchmark the Gaussian-type basis set approaches. Also, calculations employing the fixed-nuclei approximation are performed, to quantify effects due to nuclear motion. For low intensities and small ionization probabilities, we get excellent agreement of the dynamics using Gaussian-type basis sets with the all-grid solutions. Our investigations suggest that high harmonic generation (HHG) and high-frequency response, in general, can be reliably modeled using Gaussian-type basis sets for the electrons for not too high harmonics. Further, nuclear motion destroys electronic coherences in the response spectra even on the time scale of about 30 fs and affects HHG intensities, which reflect the electron dynamics occurring on the attosecond time scale. For the present system, non-Born-Oppenheimer effects are small. The Gaussian-based, nonadiabatically coupled, time-dependent multisurface approach to treat quantum electron-nuclear motion beyond the non-Born-Oppenheimer approximation can be easily extended to approximate wavefunction methods, such as time-dependent configuration interaction singles (TD-CIS), for systems where no benchmarks are available.
KW - Basis sets
KW - Chemical calculations
KW - Ionization
KW - Lasers
KW - Quantum mechanics
Y1 - 2021
U6 - https://doi.org/10.1021/acs.jctc.1c00837
SN - 1549-9618
SN - 1549-9626
VL - 17
IS - 12
SP - 7353
EP - 7365
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Rietze, Clemens
A1 - Titov, Evgenii
A1 - Granucci, Giovanni
A1 - Saalfrank, Peter
T1 - Surface hopping dynamics for azobenzene photoisomerization
BT - effects of packing density on surfaces, fluorination, and excitation wavelength
JF - The journal of physical chemistry : C, Nanomaterials and interfaces
N2 - Azobenzenes easily photoswitch in solution, while their photoisomerization at surfaces is often hindered. In recent work, it was demonstrated by nonadiabatic molecular dynamics with trajectory surface hopping [Titov et al., J. Phys. Chem. Lett. 2016, 7, 3591-3596] that the experimentally observed suppression of trans -> cis isomerization yields in azobenzenes in a densely packed SAM (self-assembled monolayer) [Gahl et al., J. Am. Chem. Soc. 2010, 132, 1831-1838] is dominated by steric hindrance. In the present work, we systematically study by ground-state Langevin and nonadiabatic surface hopping dynamics, the effects of decreasing packing density on (i) UV/vis absorption spectra, (ii) trans -> cis isomerization yields, and (iii) excited-state lifetimes of photoexcited azobenzene. Within the quantum mechanics/ molecular mechanics models adopted here, we find that above a packing density of similar to 3 molecules/nm(2), switching yields are strongly reduced, while at smaller packing densities, the "monomer limit" is quickly approached. The UV/vis absorption spectra, on the other hand, depend on packing density over a larger range (down to at least similar to 1 molecule/nm(2)). Trends for excited-state lifetimes are less obvious, but it is found that lifetimes of pi pi* excited states decay monotonically with decreasing coverage. Effects of fluorination of the switches are also discussed for single, free molecules. Fluorination leads to comparatively large trans -> cis yields, in combination with long pi pi* lifetimes. Furthermore, for selected systems, also the effects of n pi* excitation at longer excitation wavelengths have been studied, which is found to enhance trans -> cis yields for free molecules but can lead to an opposite behavior in densely packed SAMs.
KW - Computational chemistry
KW - Energy
KW - Molecules
KW - Monomers
KW - Oligomers
Y1 - 2020
U6 - https://doi.org/10.1021/acs.jpcc.0c08052
SN - 1932-7447
SN - 1932-7455
VL - 124
IS - 48
SP - 26287
EP - 26295
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Fischer, Eric W.
A1 - Werther, Michael
A1 - Bouakline, Foudhil
A1 - Saalfrank, Peter
T1 - A hierarchical effective mode approach to phonon-driven multilevel vibrational relaxation dynamics at surfaces
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistry
N2 - We discuss an efficient Hierarchical Effective Mode (HEM) representation of a high-dimensional harmonic oscillator bath, which describes phonon-driven vibrational relaxation of an adsorbate-surface system, namely, deuterium adsorbed on Si(100). Starting from the original Hamiltonian of the adsorbate-surface system, the HEM representation is constructed via iterative orthogonal transformations, which are efficiently implemented with Householder matrices. The detailed description of the HEM representation and its construction are given in the second quantization representation. The hierarchical nature of this representation allows access to the exact quantum dynamics of the adsorbate-surface system over finite time intervals, controllable via the truncation order of the hierarchy. To study the convergence properties of the effective mode representation, we solve the time-dependent Schrodinger equation of the truncated system-bath HEM Hamiltonian, with the help of the multilayer extension of the Multiconfigurational Time-Dependent Hartree (ML-MCTDH) method. The results of the HEM representation are compared with those obtained with a quantum-mechanical tier-model. The convergence of the HEM representation with respect to the truncation order of the hierarchy is discussed for different initial conditions of the adsorbate-surface system. The combination of the HEM representation with the ML-MCTDH method provides information on the time evolution of the system (adsorbate) and multiple effective modes of the bath (surface). This permits insight into mechanisms of vibration-phonon coupling of the adsorbate-surface system, as well as inter-mode couplings of the effective bath.
Y1 - 2020
U6 - https://doi.org/10.1063/5.0017716
SN - 0021-9606
SN - 1089-7690
VL - 153
IS - 6
PB - American Institute of Physics
CY - Melville
ER -
TY - GEN
A1 - Mayer, Dennis
A1 - Lever, Fabiano
A1 - Picconi, David
A1 - Metje, Jan
A1 - Ališauskas, Skirmantas
A1 - Calegari, Francesca
A1 - Düsterer, Stefan
A1 - Ehlert, Christopher
A1 - Feifel, Raimund
A1 - Niebuhr, Mario
A1 - Manschwetus, Bastian
A1 - Kuhlmann, Marion
A1 - Mazza, Tommaso
A1 - Robinson, Matthew Scott
A1 - Squibb, Richard James
A1 - Trabattoni, Andrea
A1 - Wallner, Måns
A1 - Saalfrank, Peter
A1 - Wolf, Thomas J. A.
A1 - Gühr, Markus
T1 - Following excited-state chemical shifts in molecular ultrafast x-ray photoelectron spectroscopy
T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2 - The conversion of photon energy into other energetic forms in molecules is accompanied by charge moving on ultrafast timescales. We directly observe the charge motion at a specific site in an electronically excited molecule using time-resolved x-ray photoelectron spectroscopy (TR-XPS). We extend the concept of static chemical shift from conventional XPS by the excited-state chemical shift (ESCS), which is connected to the charge in the framework of a potential model. This allows us to invert TR-XPS spectra to the dynamic charge at a specific atom. We demonstrate the power of TR-XPS by using sulphur 2p-core-electron-emission probing to study the UV-excited dynamics of 2-thiouracil. The method allows us to discover that a major part of the population relaxes to the molecular ground state within 220–250 fs. In addition, a 250-fs oscillation, visible in the kinetic energy of the TR-XPS, reveals a coherent exchange of population among electronic states.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1301
Y1 - 2022
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-577442
SN - 1866-8372
IS - 1301
ER -
TY - JOUR
A1 - Mayer, Dennis
A1 - Lever, Fabiano
A1 - Picconi, David
A1 - Metje, Jan
A1 - Ališauskas, Skirmantas
A1 - Calegari, Francesca
A1 - Düsterer, Stefan
A1 - Ehlert, Christopher
A1 - Feifel, Raimund
A1 - Niebuhr, Mario
A1 - Manschwetus, Bastian
A1 - Kuhlmann, Marion
A1 - Mazza, Tommaso
A1 - Robinson, Matthew Scott
A1 - Squibb, Richard James
A1 - Trabattoni, Andrea
A1 - Wallner, Måns
A1 - Saalfrank, Peter
A1 - Wolf, Thomas J. A.
A1 - Gühr, Markus
T1 - Following excited-state chemical shifts in molecular ultrafast x-ray photoelectron spectroscopy
JF - Nature Communications
N2 - The conversion of photon energy into other energetic forms in molecules is accompanied by charge moving on ultrafast timescales. We directly observe the charge motion at a specific site in an electronically excited molecule using time-resolved x-ray photoelectron spectroscopy (TR-XPS). We extend the concept of static chemical shift from conventional XPS by the excited-state chemical shift (ESCS), which is connected to the charge in the framework of a potential model. This allows us to invert TR-XPS spectra to the dynamic charge at a specific atom. We demonstrate the power of TR-XPS by using sulphur 2p-core-electron-emission probing to study the UV-excited dynamics of 2-thiouracil. The method allows us to discover that a major part of the population relaxes to the molecular ground state within 220–250 fs. In addition, a 250-fs oscillation, visible in the kinetic energy of the TR-XPS, reveals a coherent exchange of population among electronic states.
Y1 - 2022
U6 - https://doi.org/10.1038/s41467-021-27908-y
SN - 2041-1723
VL - 13
PB - Springer Nature
CY - Berlin
ER -
TY - JOUR
A1 - Penschke, Christopher
A1 - Edler von Zander, Robert
A1 - Beqiraj, Alkit
A1 - Zehle, Anna
A1 - Jahn, Nicolas
A1 - Neumann, Rainer
A1 - Saalfrank, Peter
T1 - Water on porous, nitrogen-containing layered carbon materials
BT - the performance of computational model chemistries
JF - Physical chemistry, chemical physics : PCCP ; a journal of European chemical societies / RSC, Royal Society of Chemistry
N2 - Porous, layered materials containing sp(2)-hybridized carbon and nitrogen atoms, offer through their tunable properties, a versatile route towards tailormade catalysts for electrochemistry and photochemistry. A key molecule interacting with these quasi two-dimensional materials (2DM) is water, and a photo(electro)chemical key reaction catalyzed by them, is water splitting into H-2 and O-2, with the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) as half reactions. The complexity of some C/N-based 2DM in contact with water raises special needs for their theoretical modelling, which in turn is needed for rational design of C/N-based catalysts. In this work, three classes of C/N-containing porous 2DM with varying pore sizes and C/N ratios, namely graphitic carbon nitride (g-C3N4), C2N, and poly(heptazine imides) (PHI), are studied with various computational methods. We elucidate the performance of different models and model chemistries (the combination of electronic structure method and basis set) for water and water fragment adsorption in the low-coverage regime. Further, properties related to the photo(electro)chemical activity like electrochemical overpotentials, band gaps, and optical excitation energies are in our focus. Specifically, periodic models will be tested vs. cluster models, and density functional theory (DFT) vs. wavefunction theory (WFT). This work serves as a basis for a systematic study of trends for the photo(electro)chemical activity of C/N-containing layered materials as a function of water content, pore size and density.
Y1 - 2022
U6 - https://doi.org/10.1039/d2cp00657j
SN - 1463-9076
SN - 1463-9084
VL - 24
IS - 24
SP - 14709
EP - 14726
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Fischer, Eric W.
A1 - Saalfrank, Peter
T1 - A thermofield-based multilayer multiconfigurational time-dependent Hartree approach to non-adiabatic quantum dynamics at finite temperature
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistry
N2 - We introduce a thermofield-based formulation of the multilayer multiconfigurational time-dependent Hartree (MCTDH) method to study finite temperature effects on non-adiabatic quantum dynamics from a non-stochastic, wave function perspective. Our approach is based on the formal equivalence of bosonic many-body theory at zero temperature with a doubled number of degrees of freedom and the thermal quasi-particle representation of bosonic thermofield dynamics (TFD). This equivalence allows for a transfer of bosonic many-body MCTDH as introduced by Wang and Thoss to the finite temperature framework of thermal quasi-particle TFD. As an application, we study temperature effects on the ultrafast internal conversion dynamics in pyrazine. We show that finite temperature effects can be efficiently accounted for in the construction of multilayer expansions of thermofield states in the framework presented herein. Furthermore, we find our results to agree well with existing studies on the pyrazine model based on the pMCTDH method.
Y1 - 2021
U6 - https://doi.org/10.1063/5.0064013
SN - 0021-9606
SN - 1089-7690
VL - 155
IS - 13
PB - American Institute of Physics
CY - Melville
ER -
TY - JOUR
A1 - Bedurke, Florian
A1 - Klamroth, Tillmann
A1 - Saalfrank, Peter
T1 - Many-electron dynamics in laser-driven molecules
BT - wavefunction theory vs. density functional theory
JF - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2 - With recent experimental advances in laser-driven electron dynamics in polyatomic molecules, the need arises for their reliable theoretical modelling. Among efficient, yet fairly accurate methods for many-electron dynamics are Time-Dependent Configuration Interaction Singles (TD-CIS) (a Wave Function Theory (WFT) method), and Real-Time Time-Dependent Density Functional Theory (RT-TD-DFT), respectively. Here we compare TD-CIS combined with extended Atomic Orbital (AO) bases, TD-CIS/AO, with RT-TD-DFT in a grid representation of the Kohn-Sham orbitals, RT-TD-DFT/Grid. Possible ionization losses are treated by complex absorbing potentials in energy space (for TD-CIS/AO) or real space (for RT-TD-DFT), respectively. The comparison is made for two test cases: (i) state-to-state transitions using resonant lasers (pi-pulses), i.e., bound electron motion, and (ii) large-amplitude electron motion leading to High Harmonic Generation (HHG). Test systems are a H-2 molecule and cis- and trans-1,2-dichlorethene, C2H2Cl2, (DCE). From time-dependent electronic energies, dipole moments and from HHG spectra, the following observations are made: first, for bound state-to-state transitions enforced by pi-pulses, TD-CIS nicely accounts for the expected population inversion in contrast to RT-TD-DFT, in agreement with earlier findings. Secondly, when using laser pulses under non-resonant conditions, dipole moments and lower harmonics in HHG spectra are obtained by TD-CIS/AO which are in good agreement with those obtained with RT-TD-DFT/Grid. Deviations become larger for higher harmonics and at low laser intensities, i.e., for low-intensity HHG signals. We also carefully test effects of basis sets for TD-CIS/AO and grid size for RT-TD-DFT/Grid, different exchange-correlation functionals in RT-TD-DFT, and absorbing boundaries. Finally, for the present examples, TD-CIS/AO is observed to be at least an order of magnitude more computationally efficient than RT-TD-DFT/Grid.
Y1 - 2021
U6 - https://doi.org/10.1039/d1cp01100f
SN - 1463-9076
SN - 1463-9084
VL - 23
IS - 24
SP - 13544
EP - 13560
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Titov, Evgenii
A1 - Sharma, Anjali
A1 - Lomadze, Nino
A1 - Saalfrank, Peter
A1 - Santer, Svetlana
A1 - Bekir, Marek
T1 - Photoisomerization of an azobenzene-containing surfactant within a micelle
JF - ChemPhotoChem
N2 - Photosensitive azobenzene-containing surfactants have attracted great attention in past years because they offer a means to control soft-matter transformations with light. At concentrations higher than the critical micelle concentration (CMC), the surfactant molecules aggregate and form micelles, which leads to a slowdown of the photoinduced trans -> cis azobenzene isomerization. Here, we combine nonadiabatic dynamics simulations for the surfactant molecules embedded in the micelles with absorption spectroscopy measurements of micellar solutions to uncover the reasons responsible for the reaction slowdown. Our simulations reveal a decrease of isomerization quantum yields for molecules inside the micelles. We also observe a reduction of extinction coefficients upon micellization. These findings explain the deceleration of the trans -> cis switching in micelles of the azobenzene-containing surfactants.
KW - azobenzene
KW - micelles
KW - photoswitches
KW - rate constants
KW - surfactants
KW - surface hopping
Y1 - 2021
U6 - https://doi.org/10.1002/cptc.202100103
SN - 2367-0932
VL - 5
IS - 10
SP - 926
EP - 932
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Sinha, Shreya
A1 - Saalfrank, Peter
T1 - "Inverted" CO molecules on NaCl(100)
BT - a quantum mechanical study
JF - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2 - Somewhat surprisingly, inverted ("O-down") CO adsorbates on NaCl(100) were recently observed experimentally after infrared vibrational excitation (Lau et al., Science, 2020, 367, 175-178). Here we characterize these species using periodic density functional theory and a quantum mechanical description of vibrations. We determine stationary points and minimum energy paths for CO inversion, for low (1/8 and 1/4 monolayers (ML)) and high (1 ML) coverages. Transition state theory is applied to estimate thermal rates for "C-down" to "O-down" isomerization and the reverse process. For the 1/4 ML p(1 x 1) structure, two-dimensional and three-dimensional potential energy surfaces and corresponding anharmonic vibrational eigenstates obtained from the time-independent nuclear Schrodinger equation are presented. We find (i) rather coverage-independent CO inversion energies (of about 0.08 eV or 8 kJ mol(-1) per CO) and corresponding classical activation energies for "C-down" to "O-down" isomerization (of about 0.15 eV or 14 kJ mol(-1) per CO); (ii) thermal isomerization rates at 22 K which are vanishingly small for the "C-down" to "O-down" isomerization but non-negligible for the back reaction; (iii) several "accidentally degenerate" pairs of eigenstates well below the barrier, each pair describing "C-down" to "O-down" localized states.
Y1 - 2020
U6 - https://doi.org/10.1039/d0cp05198e
SN - 1463-9076
SN - 1463-9084
VL - 23
IS - 13
SP - 7860
EP - 7874
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Fischer, Eric W.
A1 - Saalfrank, Peter
T1 - Ground state properties and infrared spectra of anharmonic vibrational polaritons of small molecules in cavities
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2 - Recent experiments and theory suggest that ground state properties and reactivity of molecules can be modified when placed inside a nanoscale cavity, giving rise to strong coupling between vibrational modes and the quantized cavity field. This is commonly thought to be caused either by a cavity-distorted Born-Oppenheimer ground state potential or by the formation of light-matter hybrid states, vibrational polaritons. Here, we systematically study the effect of a cavity on ground state properties and infrared spectra of single molecules, considering vibration-cavity coupling strengths from zero up to the vibrational ultrastrong coupling regime. Using single-mode models for Li-H and O-H stretch modes and for the NH3 inversion mode, respectively, a single cavity mode in resonance with vibrational transitions is coupled to position-dependent molecular dipole functions. We address the influence of the cavity mode on polariton ground state energies, equilibrium bond lengths, dissociation energies, activation energies for isomerization, and on vibro-polaritonic infrared spectra. In agreement with earlier work, we observe all mentioned properties being strongly affected by the cavity, but only if the dipole self-energy contribution in the interaction Hamiltonian is neglected. When this term is included, these properties do not depend significantly on the coupling anymore. Vibro-polaritonic infrared spectra, in contrast, are always affected by the cavity mode due to the formation of excited vibrational polaritons. It is argued that the quantized nature of vibrational polaritons is key to not only interpreting molecular spectra in cavities but also understanding the experimentally observed modification of molecular reactivity in cavities.
Y1 - 2021
U6 - https://doi.org/10.1063/5.0040853
SN - 0021-9606
SN - 1089-7690
VL - 154
IS - 10
PB - American Institute of Physics
CY - Melville
ER -
TY - JOUR
A1 - von Zander, Robert Edler
A1 - Saalfrank, Peter
T1 - On the borate-catalyzed electrochemical reduction of phosphine oxide
BT - a computational study
JF - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory
N2 - Recently, Nocera and co-workers (J. Am. Chem. Soc. 2018, 140, 13711) demonstrated that triaryl borate Lewis acids facilitate the direct electrochemical reduction of triphenylphosphine oxide (TPPO) to triphenylphosphine (TPP). In the present contribution, we report a quantum chemical study unravelling details of the reaction, which also supports the proposed ECrECi mechanism. Alternative electrochemical routes to TPPO reduction facilitated by other Lewis acids (CH3+), or by photocatalysis at semiconductor surfaces, are also briefly discussed.
Y1 - 2020
U6 - https://doi.org/10.1021/acs.jpca.0c07805
SN - 1089-5639
SN - 1520-5215
VL - 124
IS - 49
SP - 10239
EP - 10245
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Lorenz, U.
A1 - Saalfrank, Peter
T1 - A novel system-bath Hamiltonian for vibration-phonon coupling
BT - Formulation, and application to the relaxation of Si-H and Si-D bending modes of H/D:Si(100)-(2 x 1)
JF - Chemical physics : a journal devoted to experimental and theoretical research involving problems of both a chemical and physical nature
N2 - We present a rigorous method to set up a system-bath Hamiltonian for the coupling of adsorbate vibrations (the system) to surface phonons (the bath). The Hamiltonian is straightforward to derive and exact up to second order in the environment coordinates, thus capable of treating one- and two-phonon contributions to vibration-phonon coupling. The construction of the Hamiltonian uses orthogonal coordinates for system and bath modes, is based on an embedded cluster approach, and generalizes previous Hamiltonians of a similar type, but avoids several (additional) approximations. While the parametrization of the full Hamiltonian is in principle feasible by a first principles quantum mechanical treatment, here we adopt in the spirit of a QM/MM model a combination of density functional theory (“QM”, for the system) and a semiempirical forcefield (“MM”, for the bath). We apply the Hamiltonian to a fully H-covered Si(100)-(2 × 1) surface, using Fermi’s Golden Rule to obtain vibrational relaxation rates of various H–Si bending modes of this system. As in earlier work it is found that the relaxation is dominated by two-phonon contributions because of an energy gap between the Si–H bending modes and the Si phonon bands. We obtain vibrational lifetimes (of the first excited state) on the order of 2 ps at K. The lifetimes depend only little on the type of bending mode (symmetric vs. antisymmetric, parallel vs. perpendicular to the Si2H2 dimers). They decrease by a factor of about two when heating the surface to 300 K. We also study isotope effects by replacing adsorbed H atoms by deuterium, D. The Si–D bending modes are shifted into the Si phonon band of the solid, opening up one-phonon decay channels and reducing the lifetimes to few hundred fs.
Y1 - 2016
U6 - https://doi.org/10.1016/j.chemphys.2016.06.004
SN - 0301-0104
SN - 1873-4421
VL - 482
SP - 69
EP - 80
PB - Elsevier Science
CY - Amsterdam
ER -
TY - JOUR
A1 - Goulet-Hanssens, Alexis
A1 - Utecht, Manuel
A1 - Mutruc, Dragos
A1 - Titov, Evgenii
A1 - Schwarz, Jutta
A1 - Grubert, Lutz
A1 - Bleger, David
A1 - Saalfrank, Peter
A1 - Hecht, Stefan
T1 - Electrocatalytic Z -> E Isomerization of Azobenzenes
JF - Journal of the American Chemical Society
N2 - A variety of azobenzenes were synthesized to study the behavior of their E and Z isomers upon electrochemical reduction. Our results show that the radical anion of the Z isomer is able to rapidly isomerize to the corresponding E configured counterpart with a dramatically enhanced rate as compared to the neutral species. Due to a subsequent electron transfer from the formed E radical anion to the neutral Z starting material the overall transformation is catalytic in electrons; i.e., a substoichiometric amount of reduced species can isomerize the entire mixture. This pathway greatly increases the efficiency of (photo)switching while also allowing one to reach photostationary state compositions that are not restricted to the spectral separation of the individual azobenzene isomers and their quantum yields. In addition, activating this radical isomerization pathway with photoelectron transfer agents allows us to override the intrinsic properties of an azobenzene species by triggering the reverse isomerization direction (Z -> E) by the same wavelength of light, which normally triggers E -> Z isomerization. The behavior we report appears to be general, implying that the metastable isomer of a photoswitch can be isomerized to the more stable one catalytically upon reduction, permitting the optimization of azobenzene switching in new as well as indirect ways.
Y1 - 2017
U6 - https://doi.org/10.1021/jacs.6b10822
SN - 0002-7863
VL - 139
IS - 1
SP - 335
EP - 341
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Malyar, Ivan V.
A1 - Titov, Evgenii
A1 - Lomadze, Nino
A1 - Saalfrank, Peter
A1 - Santer, Svetlana
T1 - Photoswitching of azobenzene-containing self-assembled monolayers as a tool for control over silicon surface electronic properties
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2 - We report on photoinduced remote control of work function and surface potential of a silicon surface modified with a photosensitive self-assembled monolayer consisting of chemisorbed azobenzene molecules (4-nitroazobenzene). Itwas found that the attachment of the organic monolayer increases the work function by hundreds of meV due to the increase in the electron affinity of silicon substrates. The change in the work function on UV light illumination is more pronounced for the azobenzene jacketed silicon substrate (ca. 250 meV) in comparison to 50 meV for the unmodified surface. Moreover, the photoisomerization of azobenzene results in complex kinetics of thework function change: immediate decrease due to light-driven processes in the silicon surface followed by slower recovery to the initial state due to azobenzene isomerization. This behavior could be of interest for electronic devices where the reaction on irradiation should be more pronounced at small time scales but the overall surface potential should stay constant over time independent of the irradiation conditions. Published by AIP Publishing.
Y1 - 2017
U6 - https://doi.org/10.1063/1.4978225
SN - 0021-9606
SN - 1089-7690
VL - 146
PB - American Institute of Physics
CY - Melville
ER -
TY - JOUR
A1 - Xiong, Tao
A1 - Włodarczyk, Radosław Stanisław
A1 - Gallandi, Lukas
A1 - Körzdörfer, Thomas
A1 - Saalfrank, Peter
T1 - Vibrationally resolved photoelectron spectra of lower diamondoids
BT - a time-dependent approach
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistry
N2 - Vibrationally resolved lowest-energy bands of the photoelectron spectra (PES) of adamantane, diamantane, and urotropine were simulated by a time-dependent correlation function approach within the harmonic approximation. Geometries and normal modes for neutral and cationic molecules were obtained from B3LYP hybrid density functional theory (DFT). It is shown that the simulated spectra reproduce the experimentally observed vibrational finestructure (or its absence) quite well. Origins of the finestructure are discussed and related to recurrences of autocorrelation functions and dominant vibrations. Remaining quantitative and qualitative errors of the DFT-derived PES spectra refer to (i) an overall redshift by ∼0.5 eV and (ii) the absence of satellites in the high-energy region of the spectra. The former error is shown to be due to the neglect of many-body corrections to ordinary Kohn-Sham methods, while the latter has been argued to be due to electron-nuclear couplings beyond the Born-Oppenheimer approximation [Gali et al., Nat. Commun. 7, 11327 (2016)].
Y1 - 2018
U6 - https://doi.org/10.1063/1.5012131
SN - 0021-9606
SN - 1089-7690
VL - 148
IS - 4
PB - American Institute of Physics
CY - Melville
ER -
TY - JOUR
A1 - Heiden, Sophia
A1 - Yue, Yanhua
A1 - Kirsch, Harald
A1 - Wirth, Jonas A.
A1 - Saalfrank, Peter
A1 - Campen, Richard Kramer
T1 - Water dissociative adsorption on α-Al2O3(112̅0) is controlled by surface site undercoordination, density, and topology
JF - The journal of physical chemistry / publ. weekly by the American Chemical Society : C, Nanomaterials and interfaces
N2 - α-Al2O3 surfaces are common in a wide variety of applications and useful models of more complicated, environmentally abundant, alumino-silicate surfaces. While decades of work have clarified that all properties of these surfaces depend sensitively on the crystal face and the presence of even small amounts of water, quantitative insight into this dependence has proven challenging. Overcoming this challenge requires systematic study of the mechanism by which water interacts with various α-Al2O3 surfaces. Such insight is most easily gained for the interaction of small amounts of water with surfaces in ultra high vacuum. In this study, we continue our combined theoretical and experimental approach to this problem, previously applied to water interaction with the α-Al2O3 (0001) and (11̅02) surfaces, now to water interaction with the third most stable surface, that is, the (112̅0). Because we characterize all three surfaces using similar tools, it is straightforward to conclude that the (112̅0) is most reactive with water. The most important factor explaining its increased reactivity is that the high density of undercoordinated surface Al atoms on the (112̅0) surface allows the bidentate adsorption of OH fragments originating from dissociatively adsorbed water, while only monodentate adsorption is possible on the (0001) and (11̅02) surfaces: the reactivity of α-Al2O3 surfaces with water depends strongly, and nonlinearly, on the density of undercoordinated surface Al atoms.
Y1 - 2018
U6 - https://doi.org/10.1021/acs.jpcc.7b10410
SN - 1932-7447
VL - 122
IS - 12
SP - 6573
EP - 6584
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Muzdalo, Anja
A1 - Saalfrank, Peter
A1 - Vreede, Jocelyne
A1 - Santer, Mark
T1 - Cis-to-Trans Isomerization of Azobenzene Derivatives Studied with Transition Path Sampling and Quantum Mechanical/Molecular Mechanical Molecular Dynamics
JF - Journal of chemical theory and computation
N2 - Azobenzene-based molecular photoswitches are becoming increasingly important for the development of photoresponsive, functional soft-matter material systems. Upon illumination with light, fast interconversion between a more stable trans and a metastable cis configuration can be established resulting in pronounced changes in conformation, dipole moment or hydrophobicity. A rational design of functional photosensitive molecules with embedded azo moieties requires a thorough understanding of isomerization mechanisms and rates, especially the thermally activated relaxation. For small azo derivatives considered in the gas phase or simple solvents, Eyring’s classical transition state theory (TST) approach yields useful predictions for trends in activation energies or corresponding half-life times of the cis isomer. However, TST or improved theories cannot easily be applied when the azo moiety is part of a larger molecular complex or embedded into a heterogeneous environment, where a multitude of possible reaction pathways may exist. In these cases, only the sampling of an ensemble of dynamic reactive trajectories (transition path sampling, TPS) with explicit models of the environment may reveal the nature of the processes involved. In the present work we show how a TPS approach can conveniently be implemented for the phenomenon of relaxation–isomerization of azobenzenes starting with the simple examples of pure azobenzene and a push–pull derivative immersed in a polar (DMSO) and apolar (toluene) solvent. The latter are represented explicitly at a molecular mechanical (MM) and the azo moiety at a quantum mechanical (QM) level. We demonstrate for the push–pull azobenzene that path sampling in combination with the chosen QM/MM scheme produces the expected change in isomerization pathway from inversion to rotation in going from a low to a high permittivity (explicit) solvent model. We discuss the potential of the simulation procedure presented for comparative calculation of reaction rates and an improved understanding of activated states.
Y1 - 2018
U6 - https://doi.org/10.1021/acs.jctc.7b01120
SN - 1549-9618
SN - 1549-9626
VL - 14
IS - 4
SP - 2042
EP - 2051
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Melani, Giacomo
A1 - Nagata, Yuki
A1 - Wirth, Jonas
A1 - Saalfrank, Peter
T1 - Vibrational spectroscopy of hydroxylated alpha-Al2O3(0001) surfaces with and without water
BT - an ab initio molecular dynamics study
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2 - Using gradient- and dispersion-corrected density functional theory in connection with ab initio molecular dynamics and efficient, parametrized Velocity-Velocity Autocorrelation Function (VVAF) methodology, we study the vibrational spectra (Vibrational Sum Frequency, VSF, and infrared, IR) of hydroxylated alpha-Al2O3(0001) surfaces with and without additional water. Specifically, by considering a naked hydroxylated surface and the same surface with a particularly stable, "ice-like" hexagonal water later allows us to identify and disentangle main spectroscopic bands of OH bonds, their orientation and dynamics, and the role of water adsorption. In particular, we assign spectroscopic signals around 3700 cm(-1) as being dominated by perpendicularly oriented non-hydrogen bonded aluminol groups, with and without additional water. Furthermore, the thin water layer gives spectroscopic signals which are already comparable to previous theoretical and experimental findings for the solid/(bulk) liquid interface, showing that water molecules closest to the surface play a decisive role in the vibrational response of these systems. From a methodological point of view, the effects of temperature, anharmonicity, hydrogen-bonding, and structural dynamics are taken into account and analyzed, allowing us to compare the calculated IR and VSF spectra with the ones based on normal mode analysis and vibrational density of states. The VVAF approach employed in this work appears to be a computationally accurate yet feasible method to address the vibrational fingerprints and dynamical properties of water/metal oxide interfaces. Published by AIP Publishing.
Y1 - 2018
U6 - https://doi.org/10.1063/1.5023347
SN - 0021-9606
SN - 1089-7690
VL - 149
IS - 1
PB - American Institute of Physics
CY - Melville
ER -
TY - JOUR
A1 - Goulet-Hanssens, Alexis
A1 - Rietze, Clemens
A1 - Titov, Evgenii
A1 - Abdullahu, Leonora
A1 - Grubert, Lutz
A1 - Saalfrank, Peter
A1 - Hecht, Stefan
T1 - Hole Catalysis as a General Mechanism for Efficient and Wavelength-Independent Z -> E Azobenzene Isomerization
JF - CHEM
N2 - Whereas the reversible reduction of azobenzenes has been known for decades, their oxidation is destructive and as a result has been notoriously overlooked. Here, we show that a chain reaction leading to quantitative Z -> E isomerization can be initiated before reaching the destructive anodic peak potential. This hole-catalyzed pathway is accessible to all azobenzenes, without exception, and offers tremendous advantages over the recently reported reductive, radical-anionic pathway because it allows for convenient chemical initiation without the need for electrochemical setups and in the presence of air. In addition, catalytic amounts of metal-free sensitizers, such as methylene blue, can be used as excited-state electron acceptors, enabling a shift of the excitation wavelength to the far red of the azobenzene absorption (up to 660 nm) and providing quantum yields exceeding unity (up to 200%). Our approach will boost the efficiency and sensitivity of optically dense liquid-crystalline and solid photo-switchable materials.
Y1 - 2018
U6 - https://doi.org/10.1016/j.chempr.2018.06.002
SN - 2451-9294
VL - 4
IS - 7
SP - 1740
EP - 1755
PB - Cell Press
CY - Cambridge
ER -
TY - JOUR
A1 - Heiden, Sophia
A1 - Wirth, Jonas
A1 - Campen, Richard Kramer
A1 - Saalfrank, Peter
T1 - Water molecular beam scattering at alpha-Al2O3(0001)
BT - an ab initio molecular dynamics study
JF - The journal of physical chemistry : C, Nanomaterials and interfaces
N2 - Recent molecular beam experiments have shown that water may adsorb molecularly or dissociatively on an α-Al2O3(0001) surface, with enhanced dissociation probability compared to “pinhole dosing”, i.e., adsorption under thermal equilibrium conditions. However, precise information on the ongoing reactions and their relative probabilities is missing. In order to shed light on molecular beam scattering for this system, we perform ab initio molecular dynamics calculations to simulate water colliding with α-Al2O3(0001). We find that single water molecules hitting a cold, clean surface from the gas phase are either reflected, molecularly adsorbed, or dissociated (so-called 1–2 dissociation only). A certain minimum translational energy (above 0.1 eV) seems to be required to enforce dissociation, which may explain the higher dissociation probability in molecular beam experiments. When the surface is heated and/or when refined surface and beam models are applied (preadsorption with water or water fragments, clustering and internal preexcitation in the beam), additional channels open, among them physisorption, water clustering on the surface, and so-called 1–4 and 1–4′ dissociation.
Y1 - 2018
U6 - https://doi.org/10.1021/acs.jpcc.8b04179
SN - 1932-7447
VL - 122
IS - 27
SP - 15494
EP - 15504
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Ehlert, Christopher
A1 - Gühr, Markus
A1 - Saalfrank, Peter
T1 - An efficient first principles method for molecular pump-probe NEXAFS spectra
BT - application to thymine and azobenzene
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2 - Pump-probe near edge X-ray absorption fine structure (PP-NEXAFS) spectra of molecules offer insight into valence-excited states, even if optically dark. In PP-NEXAFS spectroscopy, the molecule is "pumped" by UV or visible light enforcing a valence excitation, followed by an X-ray "probe" exciting core electrons into (now) partially empty valence orbitals. Calculations of PP-NEXAFS have so far been done by costly, correlated wavefunction methods which are not easily applicable to medium-sized or large molecules. Here we propose an efficient, first principles method based on density functional theory in combination with the transition potential and Delta SCF methodology (TP-DFT/Delta SCF) to compute molecular ground state and PP-NEXAFS spectra. We apply the method to n ->pi* pump/O-K-edge NEXAFS probe spectroscopy of thymine (for which both experimental and other theoretical data exist) and to n -> pi* or pi -> pi* pump/N-K-edge NEXAFS probe spectroscopies of trans-and cis-azobenzene. Published by AIP Publishing.
Y1 - 2018
U6 - https://doi.org/10.1063/1.5050488
SN - 0021-9606
SN - 1089-7690
VL - 149
IS - 14
PB - American Institute of Physics
CY - Melville
ER -
TY - JOUR
A1 - Hänsel, Marc
A1 - Barta, Christoph
A1 - Rietze, Clemens
A1 - Utecht, Manuel Martin
A1 - Rueck-Braun, Karola
A1 - Saalfrank, Peter
A1 - Tegeder, Petra
T1 - Two-Dimensional Nonlinear Optical Switching Materials
BT - Molecular Engineering toward High Nonlinear Optical Contrasts
JF - The journal of physical chemistry : C, Nanomaterials and interfaces
N2 - Combining photochromism and nonlinear optical (NLO) properties of molecular switches-functionalized self-assembled monolayers (SAMs) represents a promising concept toward novel photonic and optoelectronic devices. Using second harmonic generation, density functional theory, and correlated wave function methods, we studied the switching abilities as well as the NLO contrasts between different molecular states of various fulgimide-containing SAMs on Si(111). Controlled variations of the linker systems as well as of the fulgimides enabled us to demonstrate very efficient reversible photoinduced ring-opening/closure reactions between the open and closed forms of the fulgimides. Thus, effective cross sections on the order of 10(-18) cm(-2) are observed. Moreover, the reversible switching is accompanied by pronounced NLO contrasts up to 32%. Further molecular engineering of the photochromic switches and the linker systems may even increase the NLO contrast upon switching.
Y1 - 2018
U6 - https://doi.org/10.1021/acs.jpcc.8b08212
SN - 1932-7447
SN - 1932-7455
VL - 122
IS - 44
SP - 25555
EP - 25564
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Xiong, Tao
A1 - Wlodarczyk, Radoslaw
A1 - Saalfrank, Peter
T1 - Vibrationally resolved absorption and fluorescence spectra of perylene and N-substituted derivatives from autocorrelation function approaches
JF - Chemical physics : a journal devoted to experimental and theoretical research involving problems of both a chemical and physical nature
N2 - Vibrationally resolved absorption and emission (fluorescence) spectra of perylene and its N-derivatives in gas phase and in solution (acetonitrile) were simulated using a time-dependent approach based on correlation functions determined by density functional theory. By systematically varying the number and position of N atoms, it is shown that the presence of nitrogen heteroatoms has a negligible effect on the molecular structure and geometric distortions upon electronic transitions, while spectral properties change: in particular the number of N atoms is important while their position is less decisive. Thus, the N-substitution can be used to fine-tune the optical properties of perylene-based molecules.
KW - Perylene
KW - Vibronic spectrum
KW - Correlation function
KW - Dimer
KW - Excimer
KW - PCM
Y1 - 2018
U6 - https://doi.org/10.1016/j.chemphys.2018.06.011
SN - 0301-0104
SN - 1873-4421
VL - 515
SP - 728
EP - 736
PB - Elsevier
CY - Amsterdam
ER -
TY - JOUR
A1 - Heiden, Sophia
A1 - Usvyat, Denis
A1 - Saalfrank, Peter
T1 - Theoretical Surface Science Beyond Gradient-Corrected Density Functional Theory
BT - Water at alpha-Al2O3(0001) as a Case Study
JF - The journal of physical chemistry : C, Nanomaterials and interfaces
N2 - The quantum chemical description of the adsorption, vibrations, and reactions of molecules at periodic solid surfaces is frequently based on a methodological "standard model": density functional theory (DFT) in the generalized gradient approximation (GGA), using plane wave bases and three-dimensional supercells. Although the computationally efficient GGA functionals can be very successful, cases are known where they do not perform so well. Most importantly, activation energies for chemical reactions are typically underestimated, with the consequence of computed reaction rates being too large. In this work, we consider a well-studied model system: water or water fragments adsorbed on an Al-terminated alpha-Al2O3(0001) surface as a test bed for studying the performance of electronic structure methods, both from DFT and wave function theory. On the DFT side, we employ two GGA exchange correlation functionals: PW91 and PBE with and without dispersion corrections, whose results are then compared to those of hybrid functionals B3LYP and HSE06. Further, we follow a periodic wave function approach in the form of local second-order Moller-Plesset perturbation theory, LMP2, on a Hartree-Fock reference. En route, we address issues arising from the choice of the basis set. The key findings of our study are as follows: (i) DFT-GGA adsorption energies are in reasonable agreement with both hybrid-DFT and LMP2 values. In particular, the deviations between the relative energies, corresponding to different adsorption structures, are in the range of the error due to missing dispersion corrections or the basis set error. (ii) Harmonic DFT-GGA vibrational frequencies for oxygen hydrogen stretch modes are by several tens of wavenumbers red-shifted compared to corresponding hybrid-DFT values. The latter are in much better agreement with recent experimental data. (iii) The activation energy for a hydrogen diffusion reaction is grossly underestimated by GGA compared to hybrid-DFT or LMP2, which in turn are quite comparable.
Y1 - 2019
U6 - https://doi.org/10.1021/acs.jpcc.9b00407
SN - 1932-7447
VL - 123
IS - 11
SP - 6675
EP - 6684
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Bedurke, Florian
A1 - Klamroth, Tillmann
A1 - Krause, Pascal
A1 - Saalfrank, Peter
T1 - Discriminating organic isomers by high harmonic generation
BT - A time-dependent configuration interaction singles study
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2 - High Harmonic Generation (HHG) is a nonlinear optical process that provides a tunable source for high-energy photons and ultrashort laser pulses. Recent experiments demonstrated that HHG spectroscopy may also be used as an analytical tool to discriminate between randomly oriented configurational isomers of polyatomic organic molecules, namely, between the cis- and trans-forms of 1,2-dichloroethene (DCE) [M. C. H. Wong et al., Phys. Rev. A 84, 051403 (2011)]. Here, we suggest as an economic and at the same time a reasonably accurate method to compute HHG spectra for polyatomic species, Time-Dependent Configuration Interaction Singles (TD-CIS) theory in combination with extended atomic orbital bases and different models to account for ionization losses. The HHG spectra are computed for aligned and unaligned cis- and trans-DCE. For the unaligned case, a coherent averaging over possible rotational orientations is introduced. Furthermore, using TD-CIS, possible differences between the HHG spectra of cis- and trans-DCE are studied. For aligned molecules, spectral differences between cis and trans emerge, which can be related to their different point group symmetries. For unaligned, randomly oriented molecules, we also find distinct HHG spectra in partial agreement with experiment. In addition to HHG response in the frequency space, we compute time-frequency HHG spectra to gain insight into which harmonics are emitted at which time. Further differences between the two isomers emerge, suggesting time-frequency HHG as another tool to discriminate configurational isomers.
Y1 - 2019
U6 - https://doi.org/10.1063/1.5096473
SN - 0021-9606
SN - 1089-7690
VL - 150
IS - 23
PB - American Institute of Physics
CY - Melville
ER -
TY - JOUR
A1 - Melani, Giacomo
A1 - Nagata, Yuki
A1 - Campen, Richard Kramer
A1 - Saalfrank, Peter
T1 - Vibrational spectra of dissociatively adsorbed D2O on Al-terminated alpha-Al2O3(0001) surfaces from ab initio molecular dynamics
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2 - Water can adsorb molecularly or dissociatively onto different sites of metal oxide surfaces. These adsorption sites can be disentangled using surface-sensitive vibrational spectroscopy. Here, we model Vibrational Sum Frequency (VSF) spectra for various forms of dissociated, deuterated water on a reconstructed, Al-terminated α-Al2O3(0001) surface at submonolayer coverages (the so-called 1-2, 1-4, and 1-4′ modes). Using an efficient scheme based on velocity-velocity autocorrelation functions, we go beyond previous normal mode analyses by including anharmonicity, mode coupling, and thermal surface motion in the framework of ab initio molecular dynamics. In this way, we calculate vibrational density of states curves, infrared, and VSF spectra. Comparing computed VSF spectra with measured ones, we find that relative frequencies of resonances are in quite good agreement and linewidths are reasonably well represented, while VSF intensities coincide not well. We argue that intensities are sensitively affected by local interactions and thermal fluctuations, even at such low coverage, while absolute peak positions strongly depend on the choice of the electronic structure method and on the appropriate inclusion of anharmonicity.
Y1 - 2019
U6 - https://doi.org/10.1063/1.5099895
SN - 0021-9606
SN - 1089-7690
VL - 150
IS - 24
PB - American Institute of Physics
CY - Melville
ER -
TY - JOUR
A1 - Bouakline, Foudhil
A1 - Fischer, E. W.
A1 - Saalfrank, Peter
T1 - A quantum-mechanical tier model for phonon-driven vibrational relaxation dynamics of adsorbates at surfaces
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2 - We present a quantum-mechanical tier model for vibrational relaxation of low-lying excited states of an adsorbate vibrational mode (system), coupled to surface phonons (bath), at zero temperature. The tier model, widely used in studies of intramolecular vibrational energy redistribution in polyatomics, is adapted here to adsorbate-surface systems with the help of an embedded cluster approach, using orthogonal coordinates for the system and bath modes, and a phononic expansion of their interaction. The key idea of the model is to organize the system-bath zeroth-order vibrational space into a hierarchical structure of vibrational tiers and keep therein only vibrational states that are sequentially generated from the system-bath initial vibrational state. Each tier is generated from the previous one by means of a successor operator, derived from the system-bath interaction Hamiltonian. This sequential procedure leads to a drastic reduction of the dimension of the system-bath vibrational space. We notably show that for harmonic vibrational motion of the system and linear system-bath couplings in the system coordinate, the dimension of the tier-model vibrational basis scales as similar to N-lxv. Here, N is the number of bath modes, l is the highest-order of the phononic expansion, and l is the size of the system vibrational basis. This polynomial scaling is computationally far superior to the exponential scaling of the original zeroth-order vibrational basis, similar to M-N, with M being the number of basis functions per bath mode. In addition, since each tier is coupled only to its adjacent neighbors, the matrix representation of the system-bath Hamiltonian in this new vibrational basis has a symmetric block-tridiagonal form, with each block being very sparse. This favors the combination of the tier-model with iterative Krylov techniques, such as the Lanczos algorithm, to solve the time-dependent Schrodinger equation for the full Hamiltonian. To illustrate the method, we study vibrational relaxation of a D-Si bending mode, coupled via two-and (mainly) one-phonon interactions to a fully D-covered Si(100)-(2 x 1) surface, using a recent first-principles system-bath Hamiltonian. The results of the tier model are compared with those obtained by the Lindblad formalism of the reduced density matrix. We find that the tier model provides much more information and insight into mechanisms of vibration-phonon couplings at surfaces, and gives more reliable estimates of the adsorbate vibrational lifetimes. Moreover, the tier model might also serve as a benchmark for other approximate quantum-dynamics methods, such as multiconfiguration wavefunction approaches. Published under license by AIP Publishing.
Y1 - 2019
U6 - https://doi.org/10.1063/1.5099902
SN - 0021-9606
SN - 1089-7690
VL - 150
IS - 24
PB - American Institute of Physics
CY - Melville
ER -
TY - JOUR
A1 - Xiong, Tao
A1 - Saalfrank, Peter
T1 - Vibrationally Broadened Optical Spectra of Selected Radicals and Cations Derived from Adamantane: A Time-Dependent Correlation Function Approach
JF - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory
N2 - Diamondoids are hydrogen-saturated molecular motifs cut out of diamond, forming a class of materials with tunable optoelectronic properties. In this work, we extend previous work on neutral, closed-shell diamondoids by computing with hybrid density functional theory and time-dependent correlation functions vibrationally broadened absorption spectra of cations and radicals derived from the simplest diamondoid, adamantane, namely, the neutral 1- and 2-adamantyl radicals (C10H15), the 1- and 2-adamantyl cations (C10H15+), and the adamantane radical cation (C10H16+). For selected cases, we also report vibrationally broadened emission, photoelectron, and resonance Raman spectra. Furthermore, the effect of the damping factor on the vibrational fine-structure is studied. The following trends are found: (1) Low-energy absorptions of the adamantyl radicals and cations, and of the adamantane cation, are all strongly red-shifted with respect to adamantane; (2) also, emission spectra are strongly red-shifted, whereas photoelectron spectra are less affected for the cases studied; (3) vibrational fine-structures are reduced compared to those of adamantane; (4) the spectroscopic signals of 1- and 2-adamantyl species are significantly different from each other; and (5) reducing the damping factor has only a limited effect on the vibrational fine-structure in most cases. This suggests that removing hydrogen atoms and/or electrons from adamantane leads to new optoelectronic properties, which should be detectable by vibronic spectroscopy.
Y1 - 2019
U6 - https://doi.org/10.1021/acs.jpca.9b03305
SN - 1089-5639
SN - 1520-5215
VL - 123
IS - 41
SP - 8871
EP - 8880
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Füchsel, Gernot
A1 - Klamroth, Tillmann
A1 - Dokic, Jadranka
A1 - Saalfrank, Peter
T1 - On the electronic structure of neutral and ionic azobenzenes and their possible role as surface mounted molecular switches
JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry
N2 - We report quantum chemical calculations, mostly based on density functional theory, on azobenzene and substituted azobenzenes as neutral molecules or ions, in ground and excited states. Both the cis and trans configurations are computed as well as the activation energies to transform one isomer into the other and the possible reaction paths and reaction surfaces along the torsion and inversion modes. All calculations are done for the isolated species, but results are discussed in light of recent experiments aiming at the switching of surface mounted azobenzenes by scanning tunneling microscopes.
Y1 - 2006
U6 - https://doi.org/10.1021/jp060969v
SN - 1520-6106
VL - 110
IS - 33
SP - 16337
EP - 16345
PB - Soc.
CY - Washington
ER -
TY - JOUR
A1 - Saalfrank, Peter
T1 - Quantum dynamical approach to ultrafast molecular desorption from surfaces
JF - Chemical reviews
Y1 - 2006
U6 - https://doi.org/10.1021/cr0501691
SN - 0009-2665
SN - 1520-6890
VL - 106
IS - 10
SP - 4116
EP - 4159
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Scholz, Robert
A1 - Lindner, Steven
A1 - Loncaric, Ivor
A1 - Tremblay, Jean Christophe
A1 - Juaristi, J.
A1 - Alducin, Maite
A1 - Saalfrank, Peter
T1 - Vibrational response and motion of carbon monoxide on Cu(100) driven by femtosecond laser pulses: Molecular dynamics with electronic friction
JF - Physical review : B, Condensed matter and materials physics
N2 - Carbon monoxide on copper surfaces continues to be a fascinating, rich microlab for many questions evolving in surface science. Recently, hot-electron mediated, femtosecond-laser pulse induced dynamics of CO molecules on Cu(100) were the focus of experiments [Inoue et al., Phys. Rev. Lett. 117, 186101 (2016)] and theory [Novko et al., Phys. Rev. Lett. 122, 016806 (2019)], unraveling details of the vibrational nonequilibrium dynamics on ultrashort (subpicoseconds) timescales. In the present work, full-dimensional time-resolved hot-electron driven dynamics are studied by molecular dynamics with electronic friction (MDEF). Dissipation is included by a friction term in a Langevin equation which describes the coupling of molecular degrees of freedom to electron-hole pairs in the copper surface, calculated from gradient-corrected density functional theory (DFT) via a local density friction approximation (LDFA). Relaxation due to surface phonons is included by a generalized Langevin oscillator model. The hot-electron induced excitation is described via a time-dependent electronic temperature, the latter derived from an improved two-temperature model. Our parameter-free simulations on a precomputed potential energy surface allow for excellent statistics, and the observed trends are confirmed by on-the-fly ab initio molecular dynamics with electronic friction (AIMDEF) calculations. By computing time-resolved frequency maps for selected molecular vibrations, instantaneous frequencies, probability distributions, and correlation functions, we gain microscopic insight into hot-electron driven dynamics and we can relate the time evolution of vibrational internal CO stretch-mode frequencies to measured data, notably an observed redshift. Quantitatively, the latter is found to be larger in MDEF than in experiment and possible reasons are discussed for this observation. In our model, in addition we observe the excitation and time evolution of large-amplitude low-frequency modes, lateral CO surface diffusion, and molecular desorption. Effects of surface atom motion and of the laser fluence are also discussed.
Y1 - 2019
U6 - https://doi.org/10.1103/PhysRevB.100.245431
SN - 2469-9950
SN - 2469-9969
VL - 100
IS - 24
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Martinazzo, Rocco
A1 - Nest, Mathias
A1 - Saalfrank, Peter
A1 - Tantardini, Gian Franco
T1 - A local coherent-state approximation to system-bath quantum dynamics
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2 - A novel quantum method to deal with typical system-bath dynamical problems is introduced. Subsystem discrete variable representation and bath coherent-state sets are used to write down a multiconfigurational expansion of the wave function of the whole system. With the help of the Dirac-Frenkel variational principle, simple equations of motion-a kind of Schrodinger-Langevin equation for the subsystem coupled to (pseudo) classical equations for the bath-are derived. True dissipative dynamics at all times is obtained by coupling the bath to a secondary, classical Ohmic bath, which is modeled by adding a friction coefficient in the derived pseudoclassical bath equations. The resulting equations are then solved for a number of model problems, ranging from tunneling to vibrational relaxation dynamics. Comparison of the results with those of exact, multiconfiguration time-dependent Hartree calculations in systems with up to 80 bath oscillators shows that the proposed method can be very accurate and might be of help in studying realistic problems with very large baths. To this end, its linear scaling behavior with respect to the number of bath degrees of freedom is shown in practice with model calculations using tens of thousands of bath oscillators.
Y1 - 2006
U6 - https://doi.org/10.1063/1.2362821
SN - 0021-9606
SN - 1089-7690
VL - 125
IS - 19
PB - American Institute of Physics
CY - Melville
ER -
TY - JOUR
A1 - Rietze, Clemens
A1 - Titov, Evgenii
A1 - Lindner, Steven
A1 - Saalfrank, Peter
T1 - Thermal isomerization of azobenzenes: on the performance of Eyring transition state theory
JF - Journal of physics : Condensed matter
N2 - The thermal Z -> E (back-) isomerization of azobenzenes is a prototypical reaction occurring in molecular switches. It has been studied for decades, yet its kinetics is not fully understood. In this paper, quantum chemical calculations are performed to model the kinetics of an experimental benchmark system, where a modified azobenzene (AzoBiPyB) is embedded in a metal-organic framework (MOF). The molecule can be switched thermally from cis to trans, under solvent-free conditions. We critically test the validity of Eyring transition state theory for this reaction. As previously found for other azobenzenes (albeit in solution), good agreement between theory and experiment emerges for activation energies and activation free energies, already at a comparatively simple level of theory, B3LYP/6-31G* including dispersion corrections. However, theoretical Arrhenius prefactors and activation entropies are in qualitiative disagreement with experiment. Several factors are discussed that may have an influence on activation entropies, among them dynamical and geometric constraints (imposed by the MOF). For a simpler model-Z -> E isomerization in azobenzene-a systematic test of quantum chemical methods from both density functional theory and wavefunction theory is carried out in the context of Eyring theory. Also, the effect of anharmonicities on activation entropies is discussed for this model system. Our work highlights capabilities and shortcomings of Eyring transition state theory and quantum chemical methods, when applied for the Z -> E (back-) isomerization of azobenzenes under solvent-free conditions.
KW - thermal isomerization
Y1 - 2017
U6 - https://doi.org/10.1088/1361-648X/aa75bd
SN - 0953-8984
SN - 1361-648X
VL - 29
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Loncaric, Ivor
A1 - Fuchsel, Gernot
A1 - Juaristi, J. I.
A1 - Saalfrank, Peter
T1 - Strong Anisotropic Interaction Controls Unusual Sticking and Scattering of CO at Ru(0001)
JF - Physical review letters
N2 - Complete sticking at low incidence energies and broad angular scattering distributions at higher energies are often observed in molecular beam experiments on gas-surface systems which feature a deep chemisorption well and lack early reaction barriers. Although CO binds strongly on Ru(0001), scattering is characterized by rather narrow angular distributions and sticking is incomplete even at low incidence energies. We perform molecular dynamics simulations, accounting for phononic (and electronic) energy loss channels, on a potential energy surface based on first-principles electronic structure calculations that reproduce the molecular beam experiments. We demonstrate that the mentioned unusual behavior is a consequence of a very strong rotational anisotropy in the molecule-surface interaction potential. Beyond the interpretation of scattering phenomena, we also discuss implications of our results for the recently proposed role of a precursor state for the desorption and scattering of CO from ruthenium.
Y1 - 2017
U6 - https://doi.org/10.1103/PhysRevLett.119.146101
SN - 0031-9007
SN - 1079-7114
VL - 119
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Andrianov, Ivan
A1 - Saalfrank, Peter
T1 - Free vibrational relaxation of H adsorbed on a Si(100) surface investigated with the multi-configurational time-dependent Hartree method
JF - Chemical physics letters
N2 - The results of a quantum-mechanical study of vibrational relaxation of hydrogen adsorbed on a Si(100) surface with the multi-configurational time-dependent Hartree (MCTDH) method are presented. A two-dimensional subsystem is coupled non-linearly to a bath of harmonic oscillators (phonons of the Si bulk), and the relaxation of subsystem vibrations proceeds primarily via a two-phonon process. Characteristic times of the system evolution agree well with our previous perturbation theory study. The vibrational population decay is non-exponential, exhibiting pronounced recurrences due to finite bath size. The dependence of the lifetimes of the vibrational levels on the bath size and on the coupling details is investigated.
Y1 - 2006
U6 - https://doi.org/10.1016/j.cplett.2006.11.067
SN - 0009-2614
VL - 433
SP - 91
EP - 96
PB - Elsevier
CY - Amsterdam
ER -
TY - JOUR
A1 - Loncaric, Ivor
A1 - Alducin, Maite
A1 - Saalfrank, Peter
A1 - Juaristi, J. I.
T1 - Femtosecond-laser-driven molecular dynamics on surfaces: Photodesorption of molecular oxygen from Ag(110)
JF - Physical review : B, Condensed matter and materials physics
N2 - We simulate the femtosecond-laser-induced desorption dynamics of a diatomic molecule from a metal surface by including the effect of the electron and phonon excitations created by the laser pulse. Following previous models, the laser-induced surface excitation is treated through the two temperature model, while the multidimensional dynamics of the molecule is described by a classical Langevin equation, in which the friction and random forces account for the action of the heated electrons. In this work we propose the additional use of the generalized Langevin oscillator model to also include the effect of the energy exchange between the molecule and the heated surface lattice in the desorption dynamics. The model is applied to study the laser-induced desorption of O-2 from the Ag(110) surface, making use of a six-dimensional potential energy surface calculated within density functional theory. Our results reveal the importance of the phonon mediated process and show that, depending on the value of the electronic density in the surroundings of the molecule adsorption site, its inclusion can significantly enhance or reduce the desorption probabilities.
Y1 - 2016
U6 - https://doi.org/10.1103/PhysRevB.93.014301
SN - 1098-0121
SN - 1550-235X
VL - 93
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Schönborn, Jan Boyke
A1 - Saalfrank, Peter
A1 - Klamroth, Tillmann
T1 - Controlling the high frequency response of H-2 by ultra-short tailored laser pulses: A time-dependent configuration interaction study
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2 - We combine the stochastic pulse optimization (SPO) scheme with the time-dependent configuration interaction singles method in order to control the high frequency response of a simple molecular model system to a tailored femtosecond laser pulse. For this purpose, we use H-2 treated in the fixed nuclei approximation. The SPO scheme, as similar genetic algorithms, is especially suited to control highly non-linear processes, which we consider here in the context of high harmonic generation. Here, we will demonstrate that SPO can be used to realize a "non-harmonic" response of H2 to a laser pulse. Specifically, we will show how adding low intensity side frequencies to the dominant carrier frequency of the laser pulse and stochastically optimizing their contribution can create a high-frequency spectral signal of significant intensity, not harmonic to the carrier frequency. At the same time, it is possible to suppress the harmonic signals in the same spectral region, although the carrier frequency is kept dominant during the optimization. (C) 2016 AIP Publishing LLC.
Y1 - 2016
U6 - https://doi.org/10.1063/1.4940316
SN - 0021-9606
SN - 1089-7690
VL - 144
PB - American Institute of Physics
CY - Melville
ER -
TY - JOUR
A1 - Ehlert, Christopher
A1 - Holzweber, Markus
A1 - Lippitz, Andreas
A1 - Unger, Wolfgang E. S.
A1 - Saalfrank, Peter
T1 - A detailed assignment of NEXAFS resonances of imidazolium based ionic liquids
JF - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2 - In Near Edge X-Ray Absorption Fine Structure (NEXAFS) spectroscopy X-Ray photons are used to excite tightly bound core electrons to low-lying unoccupied orbitals of the system. This technique offers insight into the electronic structure of the system as well as useful structural information. In this work, we apply NEXAFS to two kinds of imidazolium based ionic liquids ([C(n)C(1)im](+)[NTf2](-) and [C(4)C(1)im](+)[I](-)). A combination of measurements and quantum chemical calculations of C K and N K NEXAFS resonances is presented. The simulations, based on the transition potential density functional theory method (TP-DFT), reproduce all characteristic features observed by the experiment. Furthermore, a detailed assignment of resonance features to excitation centers (carbon or nitrogen atoms) leads to a consistent interpretation of the spectra.
Y1 - 2016
U6 - https://doi.org/10.1039/c5cp07434g
SN - 1463-9076
SN - 1463-9084
VL - 18
SP - 8654
EP - 8661
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - White, Alec F.
A1 - Heide, Chiara Josephine
A1 - Saalfrank, Peter
A1 - Head-Gordon, Martin
A1 - Luppi, Eleonora
T1 - Computation of high-harmonic generation spectra of the hydrogen molecule using time-dependent configuration-interaction
JF - Molecular physics
N2 - Here we apply and expand the knowledge developed in the case of the H atom to describe high-harmonic generation (HHG) for the H-2 molecule by using time-dependent configuration interaction with single excitations. The implications of using a finite atomic orbital basis set and the impact of a heuristic lifetime model which addresses ionisation losses are discussed. We also examine the influence of the angular momentum of the basis on the computed HHG spectra. Moreover, we discuss the impact of adding diffuse functions and ghost atoms in different geometrical configurations around the molecule. The effects of these additional centres on the HHG spectra are correlated with the physical interpretation of this nonlinear optical phenomenon as given by the three-step model, relating the maximal radial extent of the electron as predicted by the model to the radial extent of the Gaussian basis sets. [GRAPHICS] .
KW - High-harmonic generation
KW - strong field
KW - time-dependent configuration interaction
Y1 - 2016
U6 - https://doi.org/10.1080/00268976.2015.1119900
SN - 0026-8976
SN - 1362-3028
VL - 114
SP - 947
EP - 956
PB - Springer
CY - Abingdon
ER -
TY - JOUR
A1 - Wirth, Jonas
A1 - Schacht, Julia
A1 - Saalfrank, Peter
A1 - Paulus, Beate
T1 - Fluorination of the Hydroxylated alpha-Al2O3 (0001) and Its Implications for Water Adsorption: A Theoretical Study
JF - The journal of physical chemistry : C, Nanomaterials and interfaces
N2 - Fluorination of the hydroxylated alpha-Al2O3 (0001) surface is studied using periodic density functional theory calculations. On the basis of a hypothetical reaction substituting surface hydroxyl groups with fluorine atoms, we find surface fluorination to be strongly exergonic but kinetically hindered. Fluorinated surface areas turn out to be rather hydrophobic as compared to hydroxylated areas, suggesting fluorination as a potential route for tuning oxide surface properties such as hydrophilicity.
Y1 - 2016
U6 - https://doi.org/10.1021/acs.jpcc.5b10975
SN - 1932-7447
VL - 120
SP - 9713
EP - 9718
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Titov, Evgenii
A1 - Saalfrank, Peter
T1 - Exciton Splitting of Adsorbed and Free 4-Nitroazobenzene Dimers: A Quantum Chemical Study
JF - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory
N2 - Molecular photoswitches such as azobenzenes, which undergo photochemical trans <-> cis isomerizations, are often mounted for possible applications on a surface and/or surrounded by other switches, for example, in self-assembled monolayers. This may suppress the isomerization cross section due to possible steric reasons, or, as recently speculated, by exciton coupling to. neighboring switches, leading to ultrafast electronic quenching (Gahl et al., J. Am. Chem. Soc. 2010, 132, 1831). The presence of exciton coupling has been anticipated from a blue shift of the optical absorption band, compared to molecules in solution. From the theory side the need arises to properly analyze and quantify the change of absorption spectra of interacting and adsorbed switches. In particular, suitable methods should be identified, and effects of intermolecule and molecule surface interactions on spectra should be disentangled. In this paper by means of time-dependent Hartree-Fock. (TD-HF), various flavors of time-dependent density functional theory (TD-DFT), and the correlated wave function based, coupled cluster (CC2) method we investigated the 4-nitroazobenzene molecule as an:example: The low-lying singlet excited states in the isolated trans monomer and dieter as well as their composites with a silicon pentamantane nanocluster, which serves also as a crude model for a silicon surface, were determined. As most important results we found that (i) HF, CC2, range-separated density functionals, or global hybrids with large amount of exact exchange are able to describe exciton (Davydov) splitting properly, while hybrids with small amount of exact exchange fail producing spurious charge transfer. (ii) The exciton splitting in a free dimer would lead to a blue shift of the absorption signal; however, this effect is almost nullified or even overcompensated by the shift arising from van der Waals interactions between the two molecules. (iii) Adsorption on the Si "surface" leads to a further, strong red shift for the present system. (iv) At a next-nearest neighbor distance (of similar to 3.6 angstrom), the exciton splitting is similar to 0.3 eV, with or without "surface", suggesting a rapid quenching of the molecular pi ->pi* excitation. At larger distances, exciton splitting decreases rapidly.
Y1 - 2016
U6 - https://doi.org/10.1021/acs.jpca.5b10376
SN - 1089-5639
VL - 120
SP - 3055
EP - 3070
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Wirth, Jonas
A1 - Kirsch, Harald
A1 - Wlosczyk, Sebastian
A1 - Tong, Yujin
A1 - Saalfrank, Peter
A1 - Campen, Richard Kramer
T1 - Characterization of water dissociation on alpha-Al2O3(1(1)over-bar02):
theory and experiment
JF - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2 - The interaction of water with a-alumina (i.e. alpha-Al2O3) surfaces is important in a variety of applications and a useful model for the interaction of water with environmentally abundant aluminosilicate phases. Despite its significance, studies of water interaction with alpha-Al2O3 surfaces other than the (0001) are extremely limited. Here we characterize the interaction of water (D2O) with a well defined alpha-Al2O3(1 (1) over bar 02) surface in UHV both experimentally, using temperature programmed desorption and surface-specific vibrational spectroscopy, and theoretically, using periodic-slab density functional theory calculations. This combined approach makes it possible to demonstrate that water adsorption occurs only at a single well defined surface site (the so-called 1-4 configuration) and that at this site the barrier between the molecularly and dissociatively adsorbed forms is very low: 0.06 eV. A subset of OD stretch vibrations are parallel to this dissociation coordinate, and thus would be expected to be shifted to low frequencies relative to an uncoupled harmonic oscillator. To quantify this effect we solve the vibrational Schrodinger equation along the dissociation coordinate and find fundamental frequencies red-shifted by more than 1500 cm(-1). Within the context of this model, at moderate temperatures, we further find that some fraction of surface deuterons are likely delocalized: dissociatively and molecularly absorbed states are no longer distinguishable.
Y1 - 2016
U6 - https://doi.org/10.1039/c6cp01397j
SN - 1463-9076
SN - 1463-9084
VL - 18
SP - 14822
EP - 14832
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Boese, Adrian Daniel
A1 - Saalfrank, Peter
T1 - CO Molecules on a NaCl(100) Surface: Structures, Energetics, and Vibrational Davydov Splittings at Various Coverages
JF - The journal of physical chemistry : C, Nanomaterials and interfaces
N2 - In this work, we study the adsorption of CO from low to high coverage at a defect-free NaCl(100) surface by means of duster and periodic models, using highly accurate wave function-based QM:QM embedding as well as density functional theory. At low coverages, the most accurate methods predict a zero-point-corrected adsorption energy of around 13 kJ/mol, and the CO molecules are found to be oriented perpendicular to the surface. At higher coverages, lower-energy phases with nonparallel/upright, tilted orientations emerge. Besides the well-known p(2 x 1)/antiparallel phase (T/A), we find other tilted phases (tilted/irregular, T/I; tilted/spiral, T/S) as local minima. Vibrational frequencies for CO adsorbed on NaCl(100) and Davydov splittings of the C-O stretch vibration are also determined. The IR spectra are characteristic fingerprints for the relative orientation of CO molecules and may therefore be used as sensitive probes to distinguish parallel/upright from various tilted adsorption phases.
Y1 - 2016
U6 - https://doi.org/10.1021/acs.jpcc.6b03726
SN - 1932-7447
VL - 120
SP - 12637
EP - 12653
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Loncaric, Ivor
A1 - Alducin, Maite
A1 - Saalfrank, Peter
A1 - Inaki Juaristi, J.
T1 - Femtosecond laser pulse induced desorption: A molecular dynamics simulation
JF - Nature climate change
N2 - In recent simulations of femtosecond laser induced desorption of molecular oxygen from the Ag(110) surface, it has been shown that depending on the properties (depth and electronic environment) of the well in which 02 is adsorbed, the desorption can be either induced dominantly by hot electrons or via excitations of phonons. In this work we explore whether the ratios between the desorption yields from different adsorption wells can be tuned by changing initial surface temperature and laser pulse properties. We show that the initial surface temperature is an important parameter, and that by using low initial surface temperatures the electronically mediated process can be favored. In contrast, laser properties seem to have only a modest influence on the results. (C) 2016 Elsevier B.V. All rights reserved.
KW - Laser induced desorption
KW - Molecular dynamics with friction
KW - Local density friction approximation
KW - Generalized Langevin oscillator model
Y1 - 2016
U6 - https://doi.org/10.1016/j.nimb.2016.02.051
SN - 0168-583X
SN - 1872-9584
VL - 382
SP - 114
EP - 118
PB - Elsevier
CY - Amsterdam
ER -
TY - JOUR
A1 - Titov, Evgenii
A1 - Granucci, Giovanni
A1 - Goetze, Jan Philipp
A1 - Persico, Maurizio
A1 - Saalfrank, Peter
T1 - Dynamics of Azobenzene Dimer Photoisomerization: Electronic and Steric Effects
JF - The journal of physical chemistry letters
N2 - While azobenzenes readily photoswitch in solution, their photoisomerization in densely packed self-assembled monolayers (SAMs) can be suppressed. Reasons for this can be steric hindrance and/or electronic quenching, e.g., by exciton coupling. We address these possibilities by means of nonadiabatic molecular dynamics with trajectory surface hopping calculations, investigating the trans -> cis isomerization of azobenzene after excitation into the pi pi* absorption band. We consider a free monomer, an isolated dimer and a dimer embedded in a SAM-like environment of additional azobenzene molecules, imitating in this way the gradual transition from an unconstrained over an electronically coupled to an electronically coupled and sterically hindered, molecular switch. Our simulations reveal that in comparison to the single molecule the quantum yield of the trans -> cis photoisomerization is similar for the isolated dimer, but greatly reduced in the sterically constrained situation. Other implications of dimerization and steric constraints are also discussed.
Y1 - 2016
U6 - https://doi.org/10.1021/acs.jpciett.6b01401
SN - 1948-7185
VL - 7
SP - 3591
EP - 3596
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Kulesza, Alexander Jan
A1 - Titov, Evgenii
A1 - Daly, Steven
A1 - Wlodarczyk, Radoslaw
A1 - Megow, Jörg
A1 - Saalfrank, Peter
A1 - Choi, Chang Min
A1 - MacAleese, Luke
A1 - Antoine, Rodolphe
A1 - Dugourd, Philippe
T1 - Excited States of Xanthene Analogues: Photofragmentation and Calculations by CC2 and Time-Dependent Density Functional Theory
JF - ChemPhysChem : a European journal of chemical physics and physical chemistry
N2 - Action spectroscopy has emerged as an analytical tool to probe excited states in the gas phase. Although comparison of gas-phase absorption properties with quantum-chemical calculations is, in principle, straightforward, popular methods often fail to describe many molecules of interest-such as xanthene analogues. We, therefore, face their nano-and picosecond laser-induced photofragmentation with excited-state computations by using the CC2 method and time-dependent density functional theory (TDDFT). Whereas the extracted absorption maxima agree with CC2 predictions, the TDDFT excitation energies are blueshifted. Lowering the amount of Hartree-Fock exchange in the DFT functional can reduce this shift but at the cost of changing the nature of the excited state. Additional bandwidth observed in the photofragmentation spectra is rationalized in terms of multiphoton processes. Observed fragmentation from higher-lying excited states conforms to intense excited-to-excited state transitions calculated with CC2. The CC2 method is thus suitable for the comparison with photofragmentation in xanthene analogues.
KW - density functional calculations
KW - CC2 calculations
KW - multiphoton processes
KW - photofragmentation
KW - xanthenes
Y1 - 2016
U6 - https://doi.org/10.1002/cphc.201600650
SN - 1439-4235
SN - 1439-7641
VL - 17
SP - 3129
EP - 3138
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Scholz, Robert
A1 - Floss, Gereon
A1 - Saalfrank, Peter
A1 - Füchsel, Gernot
A1 - Loncaric, Ivor
A1 - Juaristi, J. I.
T1 - Femtosecond-laser induced dynamics of CO on Ru(0001): Deep insights from a hot-electron friction model including surface motion
JF - Physical review : B, Condensed matter and materials physics
N2 - A Langevin model accounting for all six molecular degrees of freedom is applied to femtosecond-laser induced, hot-electron driven dynamics of Ru(0001)(2 x 2): CO. In our molecular dynamics with electronic friction approach, a recently developed potential energy surface based on gradient-corrected density functional theory accounting for van der Waals interactions is adopted. Electronic friction due to the coupling of molecular degrees of freedom to electron-hole pairs in the metal are included via a local density friction approximation, and surface phonons by a generalized Langevin oscillator model. The action of ultrashort laser pulses enters through a substrate-mediated, hot-electron mechanism via a time-dependent electronic temperature (derived from a two-temperature model), causing random forces acting on the molecule. The model is applied to laser induced lateral diffusion of CO on the surface, "hot adsorbate" formation, and laser induced desorption. Reaction probabilities are strongly enhanced compared to purely thermal processes, both for diffusion and desorption. Reaction yields depend in a characteristic (nonlinear) fashion on the applied laser fluence, as well as branching ratios for various reaction channels. Computed two-pulse correlation traces for desorption and other indicators suggest that aside from electron-hole pairs, phonons play a non-negligible role for laser induced dynamics in this system, acting on a surprisingly short time scale. Our simulations on precomputed potentials allow for good statistics and the treatment of long-time dynamics (300 ps), giving insight into this system which hitherto has not been reached. We find generally good agreement with experimental data where available and make predictions in addition. A recently proposed laser induced population of physisorbed precursor states could not be observed with the present low-coverage model.
Y1 - 2016
U6 - https://doi.org/10.1103/PhysRevB.94.165447
SN - 2469-9950
SN - 2469-9969
VL - 94
PB - American Physical Society
CY - College Park
ER -
TY - GEN
A1 - Wirth, Jonas
A1 - Kirsch, Harald
A1 - Wlosczyk, Sebastian
A1 - Tong, Yujin
A1 - Saalfrank, Peter
A1 - Kramer Campen, Richard
T1 - Characterization of water dissociation on α-Al2O3(1102)
BT - theory and experiment
N2 - The interaction of water with α-alumina (i.e. α-Al2O3) surfaces is important in a variety of applications and a useful model for the interaction of water with environmentally abundant aluminosilicate phases. Despite its significance, studies of water interaction with α-Al2O3 surfaces other than the (0001) are extremely limited. Here we characterize the interaction of water (D2O) with a well defined α-Al2O3(1[1 with combining macron]02) surface in UHV both experimentally, using temperature programmed desorption and surface-specific vibrational spectroscopy, and theoretically, using periodic-slab density functional theory calculations. This combined approach makes it possible to demonstrate that water adsorption occurs only at a single well defined surface site (the so-called 1–4 configuration) and that at this site the barrier between the molecularly and dissociatively adsorbed forms is very low: 0.06 eV. A subset of OD stretch vibrations are parallel to this dissociation coordinate, and thus would be expected to be shifted to low frequencies relative to an uncoupled harmonic oscillator. To quantify this effect we solve the vibrational Schrödinger equation along the dissociation coordinate and find fundamental frequencies red-shifted by more than 1500 cm−1. Within the context of this model, at moderate temperatures, we further find that some fraction of surface deuterons are likely delocalized: dissociatively and molecularly absorbed states are no longer distinguishable.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 320
Y1 - 2016
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-394497
SP - 14822
EP - 14832
ER -
TY - GEN
A1 - Ehlert, Christopher
A1 - Holzweber, Markus
A1 - Lippitz, Andreas
A1 - Unger, Wolfgang E. S.
A1 - Saalfrank, Peter
T1 - A detailed assignment of NEXAFS resonances of imidazolium based ionic liquids
N2 - In Near Edge X-Ray Absorption Fine Structure (NEXAFS) spectroscopy X-Ray photons are used to excite tightly bound core electrons to low-lying unoccupied orbitals of the system. This technique offers insight into the electronic structure of the system as well as useful structural information. In this work, we apply NEXAFS to two kinds of imidazolium based ionic liquids ([CnC1im]+[NTf2]- and [C4C1im]+[I]-). A combination of measurements and quantum chemical calculations of C K and N K NEXAFS resonances is presented. The simulations, based on the transition potential density functional theory method (TP-DFT), reproduce all characteristic features observed by the experiment. Furthermore, a detailed assignment of resonance features to excitation centers (carbon or nitrogen atoms) leads to a consistent interpretation of the spectra.
T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 315
KW - ray absorption-spectroscopy
KW - fine-structure
KW - spectra
KW - simulations
KW - molecules
KW - dynamics
KW - graphene
KW - surface
KW - salts
Y1 - 2016
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-394417
SP - 8654
EP - 8661
ER -
TY - JOUR
A1 - Matis, Jochen Rene
A1 - Schoenborn, Jan Boyke
A1 - Saalfrank, Peter
T1 - A multi-reference study of the byproduct formation for a ring-closed dithienylethene photoswitch
JF - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2 - Photodriven molecular switches are sometimes hindered in their performance by forming byproducts which act as dead ends in sequences of switching cycles, leading to rapid fatigue effects. Understanding the reaction pathways to unwanted byproducts is a prerequisite for preventing them. This article presents a study of the photochemical reaction pathways for byproduct formation in the photochromic switch 1,2-bis-(3-thienyl)-ethene. Specifically, using single-and multi-reference methods the post-deexcitation reaction towards the byproduct in the electronic ground state S-0 when starting from the S-1-S-0 conical intersection (CoIn), is considered in detail. We find an unusual low-energy pathway, which offers the possibility for the formation of a dyotropic byproduct. Several high-energy pathways can be excluded with high probability.
Y1 - 2015
U6 - https://doi.org/10.1039/c5cp00987a
SN - 1463-9076
SN - 1463-9084
VL - 17
IS - 21
SP - 14088
EP - 14095
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Schulze, Michael
A1 - Utecht, Manuel Martin
A1 - Moldt, Thomas
A1 - Przyrembel, Daniel
A1 - Gahl, Cornelius
A1 - Weinelt, Martin
A1 - Saalfrank, Peter
A1 - Tegeder, Petra
T1 - Nonlinear optical response of photochromic azobenzene-functionalized self-assembled monolayers
JF - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2 - The combination of photochromic and nonlinear optical (NLO) properties of azobenzene-functionalized self-assembled monolayers (SAMs) constitutes an intriguing step towards novel photonic and optoelectronic devices. By utilizing the second-order NLO process of second harmonic generation (SHG), supported by density-functional theory and correlated wave function method calculations, we demonstrate that the photochromic interface provides the necessary prerequisites en route towards possible future technical applications: we find a high NLO contrast on the order of 16% between the switching states. These are furthermore accessible reversibly and with high efficiencies in terms of cross sections on the order of 10(-18) cm(2) for both photoisomerization reactions, i.e., drivable by means of low-power LED light sources. Finally, both photostationary states (PSSs) are thermally stable at ambient conditions.
Y1 - 2015
U6 - https://doi.org/10.1039/c5cp03093e
SN - 1463-9076
SN - 1463-9084
VL - 17
IS - 27
SP - 18079
EP - 18086
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Banerjee, Shiladitya
A1 - Stueker, Tony
A1 - Saalfrank, Peter
T1 - Vibrationally resolved optical spectra of modified diamondoids obtained from time-dependent correlation function methods
JF - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2 - Optical properties of modified diamondoids have been studied theoretically using vibrationally resolved electronic absorption, emission and resonance Raman spectra. A time-dependent correlation function approach has been used for electronic two-state models, comprising a ground state (g) and a bright, excited state (e), the latter determined from linear-response, time-dependent density functional theory (TD-DFT). The harmonic and Condon approximations were adopted. In most cases origin shifts, frequency alteration and Duschinsky rotation in excited states were considered. For other cases where no excited state geometry optimization and normal mode analysis were possible or desired, a short-time approximation was used. The optical properties and spectra have been computed for (i) a set of recently synthesized sp(2)/sp(3) hybrid species with CQC double-bond connected saturated diamondoid subunits, (ii) functionalized (mostly by thiol or thione groups) diamondoids and (iii) urotropine and other C-substituted diamondoids. The ultimate goal is to tailor optical and electronic features of diamondoids by electronic blending, functionalization and substitution, based on a molecular-level understanding of the ongoing photophysics.
Y1 - 2015
U6 - https://doi.org/10.1039/c5cp02615f
SN - 1463-9076
SN - 1463-9084
VL - 17
IS - 29
SP - 19656
EP - 19669
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Ehlert, Christopher
A1 - Kröner, Dominik
A1 - Saalfrank, Peter
T1 - A combined quantum chemical/molecular dynamics study of X-ray photoelectron spectra of polyvinyl alcohol using oligomer models
JF - Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy
N2 - X-ray photoelectron spectroscopy (XPS) is a powerful tool for probing the local chemical environment of atoms near surfaces. When applied to soft matter, such as polymers, XPS spectra are frequently shifted and broadened due to thermal atom motion and by interchain interactions. We present a combined quantum mechanical QM/molecular dynamics (MD) simulation of X-ray photoelectron spectra of polyvinyl alcohol (PVA) using oligomer models in order to account for and quantify these effects on the XPS (C1s) signal. In our study, molecular dynamics at finite temperature were performed with a classical forcefield and by ab initio MD (AIMD) using the Car-Parrinello method. Snapshots along, the trajectories represent possible conformers and/or neighbouring environments, with different C1s ionization potentials for individual C atoms leading to broadened XPS peaks. The latter are determined by Delta-Kohn Sham calculations. We also examine the experimental practice of gauging XPS (C1s) signals of alkylic C-atoms in C-containing polymers to the C1s signal of polyethylene.
We find that (i) the experimental XPS (C1s) spectra of PVA (position and width) can be roughly represented by single-strand models, (ii) interchain interactions lead to red-shifts of the XPS peaks by about 0.6 eV, and (iii) AIMD simulations match the findings from classical MD semi-quantitatively. Further, (iv) the gauging procedure of XPS (C1s) signals to the values of PE, introduces errors of about 0.5 eV. (C) 2014 Elsevier B.V. All rights reserved.
KW - Simulation of polymer XPS
KW - Delta-Kohn Sham method
KW - Thermal broadening effects
KW - Interchain interactions
KW - Classical MD
KW - Poly vinyl alcohol
Y1 - 2015
U6 - https://doi.org/10.1016/j.elspec.2014.12.007
SN - 0368-2048
SN - 1873-2526
VL - 199
SP - 38
EP - 45
PB - Elsevier
CY - Amsterdam
ER -
TY - JOUR
A1 - Schulze, Michael
A1 - Utecht, Manuel Martin
A1 - Hebert, Andreas
A1 - Rück-Braun, Karola
A1 - Saalfrank, Peter
A1 - Tegeder, Petra
T1 - Reversible Photoswitching of the Interfacial Nonlinear Optical Response
JF - The journal of physical chemistry letters
N2 - Incorporating photochromic molecules into organic/inorganic hybrid materials may lead to photoresponsive systems. In such systems, the second-order nonlinear properties can be controlled via external stimulation with light at an appropriate wavelength. By creating photochromic molecular switches containing self-assembled monolayers on Si(111), we can demonstrate efficient reversible switching, which is accompanied by a pronounced modulation of the nonlinear optical (NLO) response of the system. The concept of utilizing functionalized photoswitchable Si surfaces could be a way for the generation of two-dimensional NLO switching materials, which are promising for applications in photonic and optoelectronic devices.
Y1 - 2015
U6 - https://doi.org/10.1021/jz502477m
SN - 1948-7185
VL - 6
IS - 3
SP - 505
EP - 509
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Tong, Yujin
A1 - Wirth, Jonas
A1 - Kirsch, Harald
A1 - Wolf, Martin
A1 - Saalfrank, Peter
A1 - Campen, Richard Kramer
T1 - Optically probing Al-O and O-H vibrations to characterize water adsorption and surface reconstruction on alpha-alumina: An experimental and theoretical study
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2 - Oxide/water interfaces are ubiquitous in a wide variety of applications and the environment. Despite this ubiquity, and attendant decades of study, gaining molecular level insight into water/oxide interaction has proven challenging. In part, this challenge springs from a lack of tools to concurrently characterize changes in surface structure (i.e., water/oxide interaction from the perspective of the solid) and O-H population and local environment (i.e., water/oxide interaction from the water perspective). Here, we demonstrate the application of surface specific vibrational spectroscopy to the characterization of the interaction of the paradigmatic alpha-Al2O3(0001) surface and water. By probing both the interfacial Al-O (surface phonon) and O-H spectral response, we characterize this interaction from both perspectives. Through electronic structure calculation, we assign the interfacial Al-O response and rationalize its changes on surface dehydroxylation and reconstruction. Because our technique is all-optical and interface specific, it is equally applicable to oxide surfaces in vacuum, ambient atmospheres and at the solid/liquid interface. Application of this approach to additional alumina surfaces and other oxides thus seems likely to significantly expand our understanding of how water meets oxide surfaces and thus the wide variety of phenomena this interaction controls. (C) 2015 AIP Publishing LLC.
Y1 - 2015
U6 - https://doi.org/10.1063/1.4906346
SN - 0021-9606
SN - 1089-7690
VL - 142
IS - 5
PB - American Institute of Physics
CY - Melville
ER -
TY - JOUR
A1 - Lorenz, Ulf
A1 - Saalfrank, Peter
T1 - Measures for the non-Markovianity of a harmonic oscillator coupled to a discrete bath derived from numerically exact references
JF - The European physical journal : D, Atomic, molecular, optical and plasma physics
N2 - System-bath problems in physics and chemistry are often described by Markovian master equations. However, the Markov approximation, i.e., neglect of bath memory effects is not always justified, and different measures of non-Markovianity have been suggested in the literature to judge the validity of this approximation. Here we calculate several computable measures of non-Markovianity for the non-trivial problem of a harmonic oscillator coupled to a large number of bath oscillators. The Multi Configurational Time Dependent Hart ree nietliod is used to provide a numerically converged solution of the system-bath Schrodinger equation, from which the appropriate quantities can be calculated. In particular, we consider measures based on trace-distances and quantum discord for a variety of initial states. These quantities have proven useful in the case of two-level and other small model systems Tpically encountered in quantum optics; but are less straightforward to interpret for the more complex model systems that are relevant for chemical physics.
Y1 - 2015
U6 - https://doi.org/10.1140/epjd/e2014-50727-8
SN - 1434-6060
SN - 1434-6079
VL - 69
IS - 2
PB - Springer
CY - New York
ER -
TY - JOUR
A1 - Wirth, Jonas
A1 - Hatter, Nino
A1 - Drost, Robert
A1 - Umbach, Tobias R.
A1 - Barja, Sara
A1 - Zastrow, Matthias
A1 - Rück-Braun, Karola
A1 - Pascual, Jose Ignacio
A1 - Saalfrank, Peter
A1 - Franke, Katharina J.
T1 - Diarylethene Molecules on a Ag(111) Surface: Stability and Electron-Induced Switching
JF - The journal of physical chemistry : C, Nanomaterials and interfaces
N2 - Diarylethene derivatives are photochromic molecular switches, undergoing a ring-opening/-closing reaction by illumination with light. The symmetry of the closed form is determined by the WoodWard Hoffinann rules according to which the reaction proceeds by corirotatory rotation -in that case. Here, we show by a cOrnbined approach of scanning tunneling microscopy (STM) and density functional theory (DFT) calculations that the Open isomer of 4,4'-(4,4'-(perfluorocydopent-1-ene-1,2-diyl)bis(5-methyl-thiophent-4,2,4-dipyridine) (PDTE) retains its open form upon adsorption on a Ag(111) surface. It caribe switched into a closed form, which we identify as the digrotatOly cydization product, by controlled manipulation 'With the STM tip, Evidence of an electric-field dependent switching-process 'is interpreted on the basis of a Simple electroStatic Model, which suggests that the reaction proceedS via an "upright" intermediate state. This pathway thus strongly differs from the switching reaction in solution.
Y1 - 2015
U6 - https://doi.org/10.1021/jp5122036
SN - 1932-7447
VL - 119
IS - 9
SP - 4874
EP - 4883
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Martinez-Mesa, Aliezer
A1 - Saalfrank, Peter
T1 - Semiclassical modelling of finite-pulse effects on non-adiabatic photodynamics via initial condition filtering: The predissociation of NaI as a test case
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2 - Femtosecond-laser pulse driven non-adiabatic spectroscopy and dynamics in molecular and condensed phase systems continue to be a challenge for theoretical modelling. One of the main obstacles is the "curse of dimensionality" encountered in non-adiabatic, exact wavepacket propagation. A possible route towards treating complex molecular systems is via semiclassical surface-hopping schemes, in particular if they account not only for non-adiabatic post-excitation dynamics but also for the initial optical excitation. One such approach, based on initial condition filtering, will be put forward in what follows. As a simple test case which can be compared with exact wavepacket dynamics, we investigate the influence of the different parameters determining the shape of a laser pulse (e.g., its finite width and a possible chirp) on the predissociation dynamics of a NaI molecule, upon photoexcitation of the A(0(+)) state. The finite-pulse effects are mapped into the initial conditions for semiclassical surface-hopping simulations. The simulated surface-hopping diabatic populations are in qualitative agreement with the quantum mechanical results, especially concerning the subpicosend photoinduced dynamics, the main deviations being the relative delay of the non-adiabatic transitions in the semiclassical picture. Likewise, these differences in the time-dependent electronic populations calculated via the semiclassical and the quantum methods are found to have a mild influence on the overall probability density distribution. As a result, the branching ratios between the bound and the dissociative reaction channels and the time-evolution of the molecular wavepacket predicted by the semiclassical method agree with those computed using quantum wavepacket propagation. Implications for more challenging molecular systems are given. (C) 2015 AIP Publishing LLC.
Y1 - 2015
U6 - https://doi.org/10.1063/1.4919780
SN - 0021-9606
SN - 1089-7690
VL - 142
IS - 19
PB - American Institute of Physics
CY - Melville
ER -
TY - JOUR
A1 - Floss, Gereon
A1 - Saalfrank, Peter
T1 - The Photoinduced E -> Z Isomerization of Bisazobenzenes: A Surface Hopping Molecular Dynamics Study
JF - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory
N2 - The photoinduced E -> Z isomerization of azobenzene is a prototypical example of molecular switching. On the way toward rigid molecular rods such as those for opto-mechanical applications, multiazobenzene structures have been suggested in which several switching units are linked together within the same molecule (Bleger et al., J. Phys. Chem. B 2011, 115, 9930-9940). Large differences in the switching efficiency of multiazobenzenes have been observed, depending on whether the switching units are electronically decoupled or not. In this paper we study, on a time-resolved molecular level, the E -> Z isomerization of the simplest multiazobenzene, bisazobenzene (BAB). Two isomers (ortho- and para-BAB), differing only in the connectivity of two azo groups on a shared phenyl ring will be considered.To do so, nonadiabatic semiclassical dynamics after photo-excitation of the isomers are studied by employing an "on-the-fly", fewest switches surface hopping approach. States and couplings are calculated by Configuration Interaction (CI) based on a semiempirical (AM1) Hamiltonian (Persico and co-workers, Chem. Eur. J. 2004, 10, 2327-2341). In the case of para-BAB, computed quantum yields for photoswitching are drastically reduced compared to pristine azobenzene, due to electronic coupling of both switching units. A reason for this (apart from altered absorption spectra and reduced photochromicity) is the drastically reduced lifetimes of electronically excited states which are transiently populated. In contrast for meta-connected species, electronic subsystems are largely decoupled, and computed quantum yields are slightly higher than that for pristine azobenzene because of new isomerization channels. In this case we can also distinguish between single- and double-switch events and we find a cooperative effect: The isomerization of a single azo group is facilitated if the other azo group is already in the Z-configuration.
Y1 - 2015
U6 - https://doi.org/10.1021/acs.jpca.5b02933
SN - 1089-5639
VL - 119
IS - 20
SP - 5026
EP - 5037
PB - American Chemical Society
CY - Washington
ER -
TY - GEN
A1 - Lorenz, Ulf
A1 - Saalfrank, Peter
T1 - Comparing thermal wave function methods for multi-configuration time-dependent Hartree simulations (vol 140, 044106, 2014)
T2 - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
Y1 - 2015
U6 - https://doi.org/10.1063/1.4938051
SN - 0021-9606
SN - 1089-7690
VL - 143
IS - 22
PB - American Institute of Physics
CY - Melville
ER -
TY - JOUR
A1 - Banerjee, Shiladitya
A1 - Saalfrank, Peter
T1 - Vibrationally resolved absorption, emission and resonance Raman spectra of diamondoids: a study based on time-dependent correlation functions
JF - Physical chemistry, chemical physics : a journal of European Chemical Societies
Y1 - 2014
U6 - https://doi.org/10.1039/c3cp53535e
SN - 1463-9076
SN - 1463-9084
VL - 16
IS - 1
SP - 144
EP - 158
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Ehlert, Christopher
A1 - Unger, Wolfgang E. S.
A1 - Saalfrank, Peter
T1 - C K-edge NEXAFS spectra of graphene with physical and chemical defects: a study based on density functional theory
JF - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2 - Recently, C K-edge Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of graphite (HOPG) surfaces have been measured for the pristine material, and for HOPG treated with either bromine or krypton plasmas (Lippitz et al., Surf. Sci., 2013, 611, L1). Changes of the NEXAFS spectra characteristic for physical (krypton) and/or chemical/physical modifications of the surface (bromine) upon plasma treatment were observed. Their molecular origin, however, remained elusive. In this work we study by density functional theory, the effects of selected point and line defects as well as chemical modifications on NEXAFS carbon K-edge spectra of single graphene layers. For Br-treated surfaces, also Br 3d X-ray Photoelectron Spectra (XPS) are simulated by a cluster approach, to identify possible chemical modifications. We observe that some of the defects related to plasma treatment lead to characteristic changes of NEXAFS spectra, similar to those in experiment. Theory provides possible microscopic origins for these changes.
Y1 - 2014
U6 - https://doi.org/10.1039/c4cp01106f
SN - 1463-9076
SN - 1463-9084
VL - 16
IS - 27
SP - 14083
EP - 14095
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Wirth, Jonas
A1 - Neumann, Rainer
A1 - Antonietti, Markus
A1 - Saalfrank, Peter
T1 - Adsorption and photocatalytic splitting of water on graphitic carbon nitride: a combined first principles and semiempirical study
JF - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2 - Graphitic carbon nitride, g-C3N4, is a promising organic photo-catalyst for a variety of redox reactions. In order to improve its efficiency in a systematic manner, however, a fundamental understanding of the microscopic interaction between catalyst, reactants and products is crucial. Here we present a systematic study of water adsorption on g-C3N4 by means of density functional theory and the density functional based tight-binding method as a prerequisite for understanding photocatalytic water splitting. We then analyze this prototypical redox reaction on the basis of a thermodynamic model providing an estimate of the overpotential for both water oxidation and H+ reduction. While the latter is found to occur readily upon irradiation with visible light, we derive a prohibitive overpotential of 1.56 eV for the water oxidation half reaction, comparing well with the experimental finding that in contrast to H-2 production O-2 evolution is only possible in the presence of oxidation cocatalysts.
Y1 - 2014
U6 - https://doi.org/10.1039/c4cp02021a
SN - 1463-9076
SN - 1463-9084
VL - 16
IS - 30
SP - 15917
EP - 15926
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Kirsch, Harald
A1 - Wirth, Jonas
A1 - Tong, Yujin
A1 - Wolf, Martin
A1 - Saalfrank, Peter
A1 - Campen, Richard Kramer
T1 - Experimental characterization of unimolecular water dissociative adsorption on alpha-alumina
JF - The journal of physical chemistry : C, Nanomaterials and interfaces
N2 - alpha-Al2O3 surfaces are common in both engineered applications and the environment. Much prior work indicates that their properties, e.g., reactivity, polarity, and charge, change dramatically on interaction with water. Perhaps the simplest question that can be asked of alpha-Al2O3/water interaction is how a single water molecule interacts with the most stable alpha-Al2O3 surface: the alpha-Al2O3(0001). Over the last 15 years, a series of theoretical studies have found that water dissociatively adsorbs on alpha-Al2O3(0001) through two channels. However, to our knowledge no experimental evidence of these dissociation pathways has appeared. By combining sample preparation via supersonic molecular beam dosing, sample characterization via coherent, surface specific vibrational spectroscopy and electronic structure theory, we report the first experimental observation of reaction products of each, theoretically predicted, dissociation channel. These results thus overcome a 15 year old experiment/theory disconnect and make possible a variety of intriguing experiments that promise to provide significant new insights into water/Al2O3 and water/oxide interaction more generally.
Y1 - 2014
U6 - https://doi.org/10.1021/jp502106t
SN - 1932-7447
VL - 118
IS - 25
SP - 13623
EP - 13630
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Füchsel, Gernot
A1 - Tremblay, Jean Christophe
A1 - Saalfrank, Peter
T1 - A six-dimensional potential energy surface for Ru(0001)(2x2):CO
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2 - We present a new global ground state potential energy surface (PES) for carbon monoxide at a coverage of 1/4, on a rigid Ru(0001) surface [Ru(0001)(2x2):CO]. All six adsorbate degrees of freedom are considered. For constructing the PES, we make use of more than 90 000 points calculated with periodic density functional theory using the RPBE exchange-correlation functional and an empirical van der Waals correction. These points are used for interpolation, utilizing a symmetry-adapted corrugation reducing procedure (CRP). Three different interpolation schemes with increasing accuracy have been realized, giving rise to three flavours of the CRP PES. The CRP PES yields in agreement with the DFT reference and experiments, the atop position of CO to be the most stable adsorption geometry, for the most accurate interpolation with an adsorption energy of 1.69 eV. The CRP PES shows that diffusion parallel to the surface is hindered by a barrier of 430 meV, and that dissociation is facilitated but still activated. As a first "real" application and further test of the new potential, the six-dimensional vibrational Schrodinger equation is solved variationally to arrive at fully coupled, anharmonic frequencies and vibrational wavefunctions for the vibrating, adsorbed CO molecule. Good agreement with experiment is found also here. Being analytical, the new PES opens an efficient way towards multidimensional dynamics. (C) 2014 AIP Publishing LLC.
Y1 - 2014
U6 - https://doi.org/10.1063/1.4894083
SN - 0021-9606
SN - 1089-7690
VL - 141
IS - 9
PB - American Institute of Physics
CY - Melville
ER -
TY - JOUR
A1 - Knie, Christopher
A1 - Utecht, Manuel Martin
A1 - Zhao, Fangli
A1 - Kulla, Hannes
A1 - Kovalenko, Sergey
A1 - Brouwer, Albert M.
A1 - Saalfrank, Peter
A1 - Hecht, Stefan
A1 - Bleger, David
T1 - ortho-Fluoroazobenzenes: visible light switches with very long-lived Z isomers
JF - Chemistry - a European journal
N2 - Improving the photochemical properties of molecular photoswitches is crucial for the development of light-responsive systems in materials and life sciences. ortho-Fluoroazobenzenes are a new class of rationally designed photochromic azo compounds with optimized properties, such as the ability to isomerize with visible light only, high photoconversions, and unprecedented robust bistable character. Introducing sigma-electron-withdrawing F atoms ortho to the N=N unit leads to both an effective separation of the n -> pi* bands of the E and Z isomers, thus offering the possibility of using these two transitions for selectively inducing E/Z iso-merizations, and greatly enhanced thermal stability of the Z isomers. Additional para-electron-withdrawing groups (EWGs) work in concert with ortho-F atoms, giving rise to enhanced separation of the n -> pi* transitions. A comprehensive study of the effect of substitution on the key photochemical properties of ortho-fluoroazobenzenes is reported herein. In particular, the position, number, and nature of the EWGs have been varied, and the visible light photoconversions, quantum yields of isomerization, and thermal stabilities have been measured and rationalized by DFT calculations.
KW - azobenzenes
KW - photochromism
KW - photoswitches
KW - substituent effects
KW - visible light
Y1 - 2014
U6 - https://doi.org/10.1002/chem.201404649
SN - 0947-6539
SN - 1521-3765
VL - 20
IS - 50
SP - 16492
EP - 16501
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Saalfrank, Peter
A1 - Juaristi, J. I.
A1 - Alducin, Maite
A1 - Blanco-Rey, Maria
A1 - Muino, R. Diez
T1 - Vibrational lifetimes of hydrogen on lead films : an ab initio molecular dynamics with electronic friction (AIMDEF) study
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2 - Using density functional theory and Ab Initio Molecular Dynamics with Electronic Friction (AIMDEF), we study the adsorption and dissipative vibrational dynamics of hydrogen atoms chemisorbed on free-standing lead films of increasing thickness. Lead films are known for their oscillatory behaviour of certain properties with increasing thickness, e.g., energy and electron spill-out change in discontinuous manner, due to quantum size effects [G. Materzanini, P. Saalfrank, and P.J.D. Lindan, Phys. Rev. B 63, 235405 (2001)]. Here, we demonstrate that oscillatory features arise also for hydrogen when chemisorbed on lead films. Besides stationary properties of the adsorbate, we concentrate on finite vibrational lifetimes of H-surface vibrations. As shown by AIMDEF, the damping via vibration-electron hole pair coupling dominates clearly over the vibration-phonon channel, in particular for high-frequency modes. Vibrational relaxation times are a characteristic function of layer thickness due to the oscillating behaviour of the embedding surface electronic density. Implications derived from AIMDEF for frictional many-atom dynamics, and physisorbed species will also be given. (C) 2014 AIP Publishing LLC.
Y1 - 2014
U6 - https://doi.org/10.1063/1.4903309
SN - 0021-9606
SN - 1089-7690
VL - 141
IS - 23
PB - American Institute of Physics
CY - Melville
ER -
TY - JOUR
A1 - Utecht, Manuel Martin
A1 - Klamroth, Tillmann
A1 - Saalfrank, Peter
T1 - Optical absorption and excitonic coupling in azobenzenes forming self-assembled monolayers a study based on density functional theory
JF - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2 - Based on the analysis of optical absorption spectra, it has recently been speculated that the excitonic coupling between individual azobenzene-functionalized alkanethiols arranged in a self-assembled monolayer (SAM) on a gold surface could be strong enough to hinder collective trans-cis isomerization-on top of steric hindrance [Gahl et al., J. Am. Chem. Soc., 2010, 132, 1831]. Using models of SAMs of increasing complexity (dimer, linear N-mers, and two-dimensionally arranged N-mers) and density functional theory on the (TD-) B3LYP/6-31G* level, we determine optical absorption spectra, the nature and magnitude of excitonic couplings, and the corresponding spectral shifts. It is found that at inter-monomer distances of about 20 angstrom and above, TD-B3LYP excitation frequencies (and signal intensities) can be well described by the frequently used point-dipole approximation. Further, calculated blue shifts in optical absorption spectra account for the experimental observations made for azobenzene/gold SAMs, and hint to the fact that they can indeed be responsible for reduced switching probability in densely packed self-assembled structures.
Y1 - 2011
U6 - https://doi.org/10.1039/c1cp22793a
SN - 1463-9076
VL - 13
IS - 48
SP - 21608
EP - 21614
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Füchsel, Gernot
A1 - Klamroth, Tillmann
A1 - Monturet, Serge
A1 - Saalfrank, Peter
T1 - Dissipative dynamics within the electronic friction approach the femtosecond laser desorption of H-2/D-2 from Ru(0001)
JF - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2 - An electronic friction approach based on Langevin dynamics is used to describe the multidimensional (six-dimensional) dynamics of femtosecond laser induced desorption of H-2 and D-2 from a H(D)-covered Ru(0001) surface. The paper extends previous reduced-dimensional models, using a similar approach. In the present treatment forces and frictional coefficients are calculated from periodic density functional theory (DFT) and essentially parameter-free, while the action of femtosecond laser pulses on the metal surface is treated by using the two-temperature model. Our calculations shed light on the performance and validity of various adiabatic, non-adiabatic, and Arrhenius/Kramers type kinetic models to describe hot-electron mediated photoreactions at metal surfaces. The multidimensional frictional dynamics are able to reproduce and explain known experimental facts, such as strong isotope effects, scaling of properties with laser fluence, and non-equipartitioning of vibrational, rotational, and translational energies of desorbing species. Further, detailed predictions regarding translations are made, and the question for the controllability of photoreactions at surfaces with the help of vibrational preexcitation is addressed.
Y1 - 2011
U6 - https://doi.org/10.1039/c0cp02086a
SN - 1463-9076
VL - 13
IS - 19
SP - 8659
EP - 8670
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Tremblay, Jean Christophe
A1 - Klinkusch, Stefan
A1 - Klamroth, Tillmann
A1 - Saalfrank, Peter
T1 - Dissipative many-electron dynamics of ionizing systems
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2 - In this paper, we perform many-electron dynamics using the time-dependent configuration-interaction method in its reduced density matrix formulation (rho-TDCI). Dissipation is treated implicitly using the Lindblad formalism. To include the effect of ionization on the state-resolved dynamics, we extend a recently introduced heuristic model for ionizing states to the rho-TDCI method, which leads to a reduced density matrix evolution that is not norm-preserving. We apply the new method to the laser-driven excitation of H(2) in a strongly dissipative environment, for which the state-resolve lifetimes are tuned to a few femtoseconds, typical for dynamics of adsorbate at metallic surfaces. Further testing is made on the laser-induced intramolecular charge transfer in a quinone derivative as a model for a molecular switch. A modified scheme to treat ionizing states is proposed to reduce the computational burden associated with the density matrix propagation, and it is thoroughly tested and compared to the results obtained with the former model. The new approach scales favorably (similar to N(2)) with the number of configurations N used to represent the reduced density matrix in the rho-TDCI method, as compared to a N(3) scaling for the model in its original form.
Y1 - 2011
U6 - https://doi.org/10.1063/1.3532410
SN - 0021-9606
VL - 134
IS - 4
PB - American Institute of Physics
CY - Melville
ER -
TY - JOUR
A1 - Wirth, Jonas
A1 - Monturet, Serge
A1 - Klamroth, Tillmann
A1 - Saalfrank, Peter
T1 - Adsorption and (photo-) electrochemical splitting of water on rutile ruthenium dioxide
JF - epl : a letters journal exploring the frontiers of physics
N2 - In this work, the adsorption and splitting of the water molecule by light and/or an external potential is investigated in the frame of (photo-) electrochemical cells using a rutile ruthenium dioxide anode. With the help of periodic density functional calculations, the adsorbed structures of H(2)O and some radicals involved in the splitting process (O, OH, OOH) are obtained and compared with the available experimental results. On the basis of these electronic-structure calculations, we use a method to calculate the stability of the reaction intermediates and conclude on the thermodynamical possibility of the water splitting reaction at the surface. We demonstrate that a moderate overpotential of 0.64 V is required for the reaction to take place at the RuO(2)(110) surface.
Y1 - 2011
U6 - https://doi.org/10.1209/0295-5075/93/68001
SN - 0295-5075
VL - 93
IS - 6
PB - EDP Sciences
CY - Mulhouse
ER -
TY - JOUR
A1 - Weigel, A.
A1 - Dobryakov, A.
A1 - Klaumünzer, Bastian
A1 - Sajadi, M.
A1 - Saalfrank, Peter
A1 - Ernsting, N. P.
T1 - Femtosecond stimulated raman spectroscopy of flavin after optical excitation
JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry
N2 - In blue-light photoreceptors using flavin (BLUF), the signaling state is formed already within several 100 ps after illumination, with only small changes of the absorption spectrum. The accompanying structural evolution can, in principle, be monitored by femtosecond stimulated Raman spectroscopy (FSRS). The method is used here to characterize the excited-state properties of riboflavin and flavin adenine dinucleotide in polar solvents. Raman modes are observed in the range 90-1800 cm(-1) for the electronic ground state S-0 and upon excitation to the S-1 state, and modes >1000 cm(-1) of both states are assigned with the help of quantum-chemical calculations. Line shapes are shown to depend sensitively on resonance conditions. They are affected by wavepacket motion in any of the participating electronic states, resulting in complex amplitude modulation of the stimulated Raman spectra. Wavepackets in S-1 can be marked, and thus isolated, by stimulated-emission pumping with the picosecond Raman pulses. Excited-state absorption spectra are obtained from a quantitative comparison of broadband transient fluorescence and absorption. In this way, the resonance conditions for FSRS are determined. Early differences of the emission spectrum depend on excess vibrational energy, and solvation is seen as dynamic Stokes shift of the emission band. The ne state is evidenced only through changes of emission oscillator strength during solvation. S-1 quenching by adenine is seen with all methods in terms of dynamics, not by spectral intermediates.
Y1 - 2011
U6 - https://doi.org/10.1021/jp1117129
SN - 1520-6106
VL - 115
IS - 13
SP - 3656
EP - 3680
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Kröner, Dominik
A1 - Ehlert, Christopher
A1 - Saalfrank, Peter
A1 - Holländer, Andreas
T1 - Ab initio calculations for XPS chemical shifts of poly(vinyl-trifluoroacetate) using trimer models
JF - Surface science
N2 - X-ray photoelectron spectra (XPS) of the polymer poly(vinyl-trifluoroacetate) show C(1s) binding energy shifts which are unusual because they are influenced by atoms which are several bonds away from the probed atom. In this work, the influence of the trifluoroacetate substituent on the 1s ionization potential of the carbon atoms of the polyethylene chain is investigated theoretically using mono-substituted, diad and triad models of trimers representing the polymer. Carbon 1s ionization energies are calculated by the Hartree-Fock theory employing Koopmans' theorem. The influence of the configuration and conformation of the functional groups as well as the degree of substitution are found to be important determinants of XPS spectra. It is further found that the 1s binding energy correlates in a linear fashion, with the total electrostatic potential at the position of the probe atom, and depends not only on nearest neighbor effects. This may have implications for the interpretation of high-resolution XP spectra.
KW - Ab initio quantum chemical methods and calculations
KW - X-ray photoelectron spectroscopy
KW - Insulating films
Y1 - 2011
U6 - https://doi.org/10.1016/j.susc.2011.05.021
SN - 0039-6028
VL - 605
IS - 15-16
SP - 1516
EP - 1524
PB - Elsevier
CY - Amsterdam
ER -
TY - JOUR
A1 - Luo, Ying
A1 - Utecht, Manuel Martin
A1 - Dokic, Jadranka
A1 - Korchak, Sergey
A1 - Vieth, Hans-Martin
A1 - Haag, Rainer
A1 - Saalfrank, Peter
T1 - Cis-trans isomerisation of substituted aromatic imines a comparative experimental and theoretical study
JF - ChemPhysChem : a European journal of chemical physics and physical chemistry
N2 - The cis-trans isomerisation of N-benzylideneaniline (NBA) and derivatives containing a central C=N bond has been investigated experimentally and theoretically. Eight different NBA molecules in three different solvents were irradiated to enforce a photochemical trans (hv) -> cis isomerisation and the kinetics of the thermal backreaction cis (Delta)-> trans were determined by NMR spectroscopy measurements in the temperature range between 193 and 288 K. Theoretical calculations using density functional theory and Eyring transition-state theory were carried out for 12 different NBA species in the gas phase and three different solvents to compute thermal isomerisation rates of the thermal back reaction. While the computed absolute rates are too large, they reveal and explain experimental trends. Time-dependent density functional theory provides optical spectra for vertical transitions and excitation energy differences between trans and cis forms. Together with isomerisation rates, the latter can be used to identify "optimal switches" with good photochromicity and reasonable thermal stability.
KW - density functional calculations
KW - imines
KW - isomerization
KW - photochemistry
KW - thermochemistry
Y1 - 2011
U6 - https://doi.org/10.1002/cphc.201100179
SN - 1439-4235
VL - 12
IS - 12
SP - 2311
EP - 2321
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Bleger, David
A1 - Dokic, Jadranka
A1 - Peters, Maike V.
A1 - Grubert, Lutz
A1 - Saalfrank, Peter
A1 - Hecht, Stefan
T1 - Electronic decoupling approach to quantitative photoswitching in linear multiazobenzene architectures
JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry
N2 - A strategy to optimize the photoswitching efficiency of rigid, linear multiazobenzene constructs is presented. It consists of introducing large dihedral angles between azobenzene moieties linked via aryl-aryl connections in their para positions. Four bisazobenzenes exhibiting different dihedral angles as well as three single azobenzene reference compounds have been synthesized, and their switching behavior has been studied as well as experimentally and theoretically analyzed. As the dihedral angle between the two azobenzene units increases and consequently the electronic conjugation decreases, the photochromic characteristics improve, finally leading to individual azobenzene switches operating independently in the case of the perpendicular ortho,ortho,ortho',ortho'-tetramethyl biphenyl linker. The electronic decoupling leads to efficient separation of the absorption spectra of the involved switching states and hence by choosing the appropriate irradiation wavelength, an almost quantitative E -> Z photoisomerization up to 97% overall Z-content can be achieved. In addition, thermal Z -> E isomerization processes become independent of each other with increasing decoupling. The electronic decoupling could furthermore be proven by electrochemistry. The experimental data are supported by theory, and calculations additionally provide mechanistic insight into the preferred pathway for the thermal Z,Z -> Z,E -> E,E isomerization via inversion on the inner N-atoms. Our decoupling approach outlined herein provides the basis for constructing rigid rod architectures composed of multiple azobenzene photochromes, which display practically quantitative photoswitching properties, a necessary prerequisite to achieve highly efficient transduction of light energy directly into motion.
Y1 - 2011
U6 - https://doi.org/10.1021/jp2044114
SN - 1520-6106
VL - 115
IS - 33
SP - 9930
EP - 9940
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Klaumünzer, Bastian
A1 - Kröner, Dominik
A1 - Lischka, Hans
A1 - Saalfrank, Peter
T1 - Non-adiabatic excited state dynamics of riboflavin after photoexcitation
JF - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2 - Flavins are chromophores in light-gated enzymes and therefore central in many photobiological processes. To unravel the optical excitation process as the initial, elementary step towards signal transduction, detailed ultrafast (femtosecond) experiments probing the photo-activation of flavins have been carried out recently [Weigel et al., J. Phys. Chem. B, 2011, 115, 3656-3680.]. The present paper contributes to a further understanding and interpretation of these experiments by studying the post-excitation vibrational dynamics of riboflavin (RF) and microsolvated riboflavin, RF center dot 4H(2)O, using first principles non-adiabatic molecular dynamics. By analyzing the characteristic atom motions and calculating time-resolved stimulated emission spectra following pi pi* excitation, it is found that after optical excitation C-N and C-C vibrations in the isoalloxazine rings of riboflavin set in. The Franck-Condon (vertically excited) state decays within about 10 fs, in agreement with experiment. Anharmonic coupling leads to Intramolecular Vibrational energy Redistribution (IVR) on the timescale of about 80-100 fs, first to (other) C-C stretching modes of the isoalloxazine rings, then by energy spread over the whole molecule, including low-frequency in-plane modes. The IVR is accompanied by a red-shift and broadening of the emission spectrum. When RF is microsolvated with four water molecules, an overall redshift of optical spectra by about 20 nm is observed but the relaxation dynamics is only slightly affected. For several trajectories, a tendency for hydrogen transfer from water to flavin-nitrogen (N-5) was found.
Y1 - 2012
U6 - https://doi.org/10.1039/c2cp40978j
SN - 1463-9076
VL - 14
IS - 24
SP - 8693
EP - 8702
PB - Royal Society of Chemistry
CY - Cambridge
ER -
TY - JOUR
A1 - Zenichowski, Karl
A1 - Dokic, Jadranka
A1 - Klamroth, Tillmann
A1 - Saalfrank, Peter
T1 - Current versus temperature-induced switching of a single molecule - open-system density matrix theory for 1,5-cyclooctadiene on Si(100)
JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2 - The switching of single cyclooctadiene molecules chemisorbed on a Si(100) surface between two stable conformations, can be achieved with a scanning tunneling microscope [Nacci , Phys. Rev. B 77, 121405(R) (2008)]. Recently, it was shown by quantum chemical and quantum dynamical simulations that major experimental facts can be explained by a single-mode model with switching enforced by inelastic electron tunneling (IET) excitations and perturbed by vibrational relaxation [Nacci , Nano Lett. 9, 2997 (2009)]. In the present paper, we extend the previous theoretical work in several respects: (1) The model is generalized to a two-mode description in which two C2H4 units of COD can move independently; (2) contributions of dipole and, in addition, (cation and anion) resonance-IET rates are considered; (3) the harmonic-linear vibrational relaxation model used previously is generalized to anharmonic vibrations. While the present models highlight generic aspects of IET-switching between two potential minima, they also rationalize specific experimental findings for COD/Si(100): (1) A single-electron excitation mechanism with a linear dependence of the switching rate on tunneling current I, (2) the capability to switch both at negative and positive sample biases, and (3) a crossover temperature around similar to 60 K from an IET-driven, T-independent atom tunneling regime, to classical over-the-barrier isomerization with exponential T-dependence at higher temperatures for a bias voltage of +1.5 V and an average tunneling current of 0.73 nA.
Y1 - 2012
U6 - https://doi.org/10.1063/1.3692229
SN - 0021-9606
VL - 136
IS - 9
PB - American Institute of Physics
CY - Melville
ER -
TY - JOUR
A1 - Götze, Jan Philipp
A1 - Saalfrank, Peter
T1 - Quantum chemical modeling of the kinetic isotope effect of the carboxylation step in RuBisCO
JF - Journal of molecular modeling
N2 - Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), the most important enzyme for the assimilation of carbon into biomass, features a well-known isotope effect with regards to the CO2 carbon atom. This kinetic isotope effect alpha = k (12)/k (13) for the carboxylation step of the RuBisCO reaction sequence, and its microscopic origin, was investigated with the help of cluster models and quantum chemical methods [B3LYP/6-31G(d,p)]. We use a recently proposed model for the RuBisCO active site, in which a water molecule remains close to the reaction center during carboxylation of ribulose-1,5-bisphosphate [B. Kannappan, J.E. Gready, J. Am. Chem. Soc. 130 (2008), 15063]. Alternative active-site models and/or computational approaches were also tested. An isotope effect alpha for carboxylation is found, which is reasonably close to the one measured for the overall reaction, and which originates from a simple frequency shift of the bending vibration of (CO2)-C-12 compared to (CO2)-C-13. The latter is the dominant mode for the product formation at the transition state.
KW - Cluster model
KW - Dark reactions
KW - Densityfunctional theory
KW - Isotope effect
KW - Photosynthesis
KW - Quantum chemistry
KW - RuBisCO
Y1 - 2012
U6 - https://doi.org/10.1007/s00894-011-1207-0
SN - 1610-2940
VL - 18
IS - 5
SP - 1877
EP - 1883
PB - Springer
CY - New York
ER -
TY - JOUR
A1 - Füchsel, Gernot
A1 - Tremblay, Jean Christophe
A1 - Klamroth, Tillmann
A1 - Saalfrank, Peter
T1 - Selective excitation of molecule-surface vibrations in H2 and D2 dissociatively adsorbed on Ru(0001)
JF - Israel journal of chemistry
N2 - In this contribution we report about the selective vibrational excitation of H2 and D2 on Ru(0001) as an example for nonadiabatic coupling of an open quantum system to a dissipative environment. We investigate the possibility of achieving state-selective vibrational excitations of H2 and D2 adsorbed on a Ru(0001) surface using picosecond infrared laser pulses. The systems behavior is explored using pulses that are rationally designed and others that are optimized using a time-local variant of Optimal Control Theory. The effects of dissipation on the laser-driven dynamics are studied using the reduced-density matrix formalism. The non-adiabatic couplings between adsorbate and surface are computed perturbatively, for which our recently introduced state-resolved anharmonic rate model is used. It is shown that mode- and state-selective excitation can be achieved in the absence of dissipation when using optimized laser pulses. The inclusion of dissipation in the model reduces the state selectivity and the population transfer yield to highly excited states. In this case, mode activation is most effectively realized by a rational pulse of carefully chosen duration rather than by a locally optimized pulse.
KW - dissipative dynamics
KW - photochemistry
KW - quantum control
KW - surface chemistry
Y1 - 2012
U6 - https://doi.org/10.1002/ijch.201100097
SN - 0021-2148
VL - 52
IS - 5
SP - 438
EP - 451
PB - Wiley-VCH
CY - Weinheim
ER -
TY - JOUR
A1 - Tremblay, Jean Christophe
A1 - Füchsel, Gernot
A1 - Saalfrank, Peter
T1 - Excitation, relaxation, and quantum diffusion of CO on copper
JF - Physical review : B, Condensed matter and materials physics
N2 - We investigate the effect of intermode coupling and anharmonicity on the excitation and relaxation dynamics of CO on Cu(100). The nonadiabatic coupling of the adsorbate to the surface is treated perturbatively using a position-dependent state-resolved transition rate model. Using the potential energy surface of Marquardt et al. [J. Chem. Phys. 132, 074108 (2010)], which provides an accurate description of intermode interactions, we propose a four-dimensional model that represents simultaneously the diffusion and the desorption of the adsorbate. The system is driven by both rational and optimized infrared laser pulses to favor either selective mode and state excitations or lateral displacement along the diffusion coordinate. The dissipative dynamics is simulated using the reduced density matrix in its Lindblad form. We show that coupling between the degrees of freedom, mediated by the creation and annihilation of electron-hole pairs in the metal substrate, significantly affects the system excitation and relaxation dynamics. In particular, the angular degrees of freedom appear to play an important role in the energy redistribution among the molecule-surface vibrations. We also show that coherent excitation using simple IR pulses can achieve population transfer to a specific target to some extent but does not allow enforcement of the directionality to the diffusion motion.
Y1 - 2012
U6 - https://doi.org/10.1103/PhysRevB.86.045438
SN - 1098-0121
SN - 1550-235X
VL - 86
IS - 4
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Bronner, C.
A1 - Leyssner, F.
A1 - Stremlau, S.
A1 - Utecht, Manuel Martin
A1 - Saalfrank, Peter
A1 - Klamroth, Tillmann
A1 - Tegeder, P.
T1 - Electronic structure of a subnanometer wide bottom-up fabricated graphene nanoribbon: End states, band gap, and dispersion
JF - Physical review : B, Condensed matter and materials physics
N2 - Angle-resolved two-photon photoemission and high-resolution electron energy loss spectroscopy are employed to derive the electronic structure of a subnanometer atomically precise quasi-one-dimensional graphene nanoribbon (GNR) on Au(111). We resolved occupied and unoccupied electronic bands including their dispersion and determined the band gap, which possesses an unexpectedly large value of 5.1 eV. Supported by density functional theory calculations for the idealized infinite polymer and finite size oligomers, an unoccupied nondispersive electronic state with an energetic position in the middle of the band gap of the GNR could be identified. This state resides at both ends of the ribbon (end state) and is only found in the finite sized systems, i.e., the oligomers.
Y1 - 2012
U6 - https://doi.org/10.1103/PhysRevB.86.085444
SN - 1098-0121
VL - 86
IS - 8
PB - American Physical Society
CY - College Park
ER -
TY - JOUR
A1 - Zenichowski, Karl
A1 - Nacci, Ch
A1 - Fölsch, S.
A1 - Dokic, Jadranka
A1 - Klamroth, Tillmann
A1 - Saalfrank, Peter
T1 - STM-switching of organic molecules on semiconductor surfaces: an above threshold density matrix model for 1,5 cyclooctadiene on Si(100)
JF - Journal of physics : Condensed matter
N2 - The scanning tunnelling microscope (STM)-induced switching of a single cyclooctadiene molecule between two stable conformations chemisorbed on a Si(100) surface is investigated using an above threshold model including a neutral ground state and an ionic excited state potential. Switching was recently achieved experimentally with an STM operated at cryogenic temperatures (Nacci et al 2008 Phys. Rev. B 77 121405(R)) and rationalized by a below threshold model using just a single potential energy surface (Nacci et al 2009 Nano Lett. 9 2997).
In the present paper, we show that experimental key findings on the inelastic electron tunnelling (IET) switching can also be rationalized using an above threshold density matrix model, which includes, in addition to the neutral ground state potential, an anionic or cationic excited potential. We use one and two-dimensional potential energy surfaces. Furthermore, the influence of two key parameters of the density matrix description, namely the electronic lifetime of the ionic resonance and the vibrational lifetimes, on the ground state potential are discussed.
Y1 - 2012
U6 - https://doi.org/10.1088/0953-8984/24/39/394009
SN - 0953-8984
VL - 24
IS - 39
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Bouakline, Foudhil
A1 - Lüder, Franziska
A1 - Martinazzo, Rocco
A1 - Saalfrank, Peter
T1 - Reduced and exact quantum dynamics of the vibrational relaxation of a molecular system interacting with a finite-dimensional bath
JF - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory
N2 - We investigate the vibrational relaxation of a Morse oscillator, nonlinearly coupled to a finite-dimensional bath of harmonic oscillators at zero temperature, using two different approaches: Reduced dynamics with the help of the Lindblad formalism of reduced density matrix theory in combination with Fermi's Golden Rule, and exact dynamics (within the chosen model). with the multiconfiguration time-dependent Hartree (MCTDH) method. Two different models have been constructed, the situation where the bath spectrum is exactly resonant with the anharmonic oscillator transition frequencies, and the case for which the subsystem is slightly off-resonant with the environment. At short times, reduced dynamics calculations describe the relaxation process qualitatively well but fail to reproduce recurrences observed with MCTDH for longer times. Lifetimes of all the vibrational levels of the Morse oscillator have been calculated, and both Lindblad and MCTDH. results show the same dependence of the lifetimes on the initial vibrational state quantum number. A prediction, which should be generic for adsorbate systems is a striking, sharp increase of lifetimes of the subsystem vibrational levels close to the dissociation This is contradictory with harmonic/linear extrapolation laws, which predict a monotonic decrease of the lifetime with initial vibrational quantum number.
Y1 - 2012
U6 - https://doi.org/10.1021/jp304466u
SN - 1089-5639
VL - 116
IS - 46
SP - 11118
EP - 11127
PB - American Chemical Society
CY - Washington
ER -