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  - 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  - 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  - 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  - 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  - 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  - GEN
A1  - Banerjee, Shiladitya
A1  - Stüker, Tony
A1  - Saalfrank, Peter
T1  - Vibrationally resolved optical spectra of modified diamondoids obtained from time-dependent correlation function methods
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 sp2/sp3 hybrid species with C[double bond, length as m-dash]C 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.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 211 
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-86826
ER  - 
TY  - JOUR
A1  - Banerjee, Shiladitya
A1  - Stüker, Tony
A1  - Saalfrank, Peter
T1  - Vibrationally resolved optical spectra of modified diamondoids obtained from time-dependent correlation function methods
JF  - Physical chemistry, chemical physics : PCCP ; 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 sp2/sp3 hybrid species with C[double bond, length as m-dash]C 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  - 1463-9084
SN  - 1463-9076
VL  - 17
IS  - 29
SP  - 19656
EP  - 19669
PB  - Royal Society of Chemistry
CY  - Cambridge
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  - Banerjee, Shiladitya
A1  - Saalfrank, Peter
T1  - Vibrationally resolved absorption, emission and resonance Raman spectra of diamondoids : a study based on time- dependent correlation functions
Y1  - 2014
UR  - http://pubs.rsc.org/en/content/articlehtml/2014/cp/c3cp53535e
U6  - https://doi.org/10.1039/C3CP53535E
ER  - 
TY  - GEN
A1  - Banerjee, Shiladitya
A1  - Saalfrank, Peter
T1  - Vibrationally resolved absorption, emission and resonance Raman spectra of diamondoids
BT  - a study based on time-dependent correlation functions
N2  - The time-dependent approach to electronic spectroscopy, as popularized by Heller and coworkers in the 1980's, is applied here in conjunction with linear-response, time-dependent density functional theory to study vibronic absorption, emission and resonance Raman spectra of several diamondoids. Two-state models, the harmonic and the Condon approximations, are used for the calculations, making them easily applicable to larger molecules. The method is applied to nine pristine lower and higher diamondoids: adamantane, diamantane, triamantane, and three isomers each of tetramantane and pentamantane. We also consider a hybrid species “Dia = Dia” – a shorthand notation for a recently synthesized molecule comprising two diamantane units connected by a C[double bond, length as m-dash]C double bond. We resolve and interpret trends in optical and vibrational properties of these molecules as a function of their size, shape, and symmetry, as well as effects of “blending” with sp2-hybridized C-atoms. Time-dependent correlation functions facilitate the computations and shed light on the vibrational dynamics following electronic transitions.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 238 
KW  - adamantane
KW  - models
KW  - molecules
KW  - states
KW  - thermochemistry
Y1  - 2013
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-94542
SP  - 144
EP  - 158
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  - 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  - 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  - 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  - 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  - 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  - 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  - 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. <br /> [GRAPHICS] <br /> .
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  - Paramonov, Guennaddi K.
A1  - Saalfrank, Peter
T1  - Time-evolution operator method for non-Markovian density matrix propagation in time and space representation : application to laser association of OH in an environment
N2  - An efficient method for the numerical solution of a non-Markovian, open-system density matrix equation of motion in coordinate representation is developed. We apply the scheme to model simulations of the laser-assisted O+H -> OH association reaction in an environment. The suggested approach is based on the application of the time-evolution operator to the "closed-system" part of the overall Hamiltonian and transformation of the open-system equation of motion to the Heisenberg picture suitable for numerical propagation. A dual role of the system-environment coupling with respect to the infrared (ir) laser-driven association of OH is demonstrated: the association probability is increased due to the coupling at relatively weak laser fields, but decreased at strong laser fields. Moreover, at a certain strength of the ir laser field, the association probability does not depend on the strength of the system-bath coupling at all.
Y1  - 2009
UR  - http://pra.aps.org/
U6  - https://doi.org/10.1103/Physreva.79.013415
SN  - 1050-2947
ER  - 
TY  - JOUR
A1  - Tremblay, Jean Christophe
A1  - Krause, Pascal
A1  - Klamroth, Tillmann
A1  - Saalfrank, Peter
T1  - Time-dependent response of dissipative electron systems
N2  - We present a systematic study of the influence of energy and phase relaxation on dynamic polarizability simulations in the linear response regime. The nonperturbative approach is based on explicit electron dynamics using short laser pulses of low intensities. To include environmental effects on the property calculation, we use the time- dependent configuration-interaction method in its reduced density matrix formulation. Both energy dissipation and nonlocal pure dephasing are included. The explicit treatment of time-resolved electron dynamics gives access to the phase shift between the electric field and the induced dipole moment, which can be used to define a useful uncertainty measure for the dynamic polarizability. The nonperturbative treatment is compared to perturbation theory expressions, as applied to a simple model system, the rigid H-2 molecule. It is shown that both approaches are equivalent for low field intensities, but the time-dependent treatment provides complementary information on the phase of the induced dipole moment, which allows for the definition of an uncertainty associated with the computation of the dynamic polarizability in the linear response regime.
Y1  - 2010
UR  - http://pra.aps.org/
U6  - https://doi.org/10.1103/Physreva.81.063420
SN  - 1050-2947
ER  - 
TY  - JOUR
A1  - Krause, Pascal
A1  - Klamroth, Tillmann
A1  - Saalfrank, Peter
T1  - Time-dependent configuration-interaction calculations of laser-pulse-driven many-electron dynamics : Controlled dipole switching in lithium cyanide
N2  - We report simulations of laser-driven many-electron dynamics by means of the time-dependent configuration interaction singles (doubles) approach. The method accounts for the correlation of ground and excited states, is capable of describing explicitly time-dependent, nonlinear phenomena, and is systematically improvable. Lithium cyanide serves as a molecular test system in which the charge distribution and hence the dipole moment are shown to be switchable, in a controlled fashion, by (a series of) laser pulses which induce selective, state-to-state electronic transitions. One focus of our time-dependent calculations is the question of how fast the transition from the ionic ground state to a specific excited state that is embedded in a multitude of other states can be made, without creating an electronic wave packet. (c) 2005 American Institute of Physics
Y1  - 2005
SN  - 0021-9606
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  - Saalfrank, Peter
T1  - Theory of photon- and STM-induced bond cleavage at surfaces
N2  - In this contribution, recent advances in the theory of laser and, to a lesser extent, of scanning tunneling microscope (STM) induced cleavage of bonds between an adsorbate and a solid surface, will be reviewed. Special emphasis will be given to the quantum dynamics of electronically non-adiabatic reactions. (c) 2005 Elsevier Ltd. All rights reserved
Y1  - 2004
SN  - 1359-0286
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  - 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  - JOUR
A1  - Nest, Mathias
A1  - Klamroth, Tillmann
A1  - Saalfrank, Peter
T1  - The multiconfiguration time-dependent Hartree-Fock method for quantum chemical calculations
N2  - We apply the multiconfiguration time-dependent Hartree-Fock method to electronic structure calculations and show that quantum chemical information can be obtained with this explicitly time-dependent approach. Different equations of motion are discussed, as well as the numerical cost. The two-electron integrals are calculated using a natural potential expansion, of which we describe the convergence behavior in detail
Y1  - 2005
SN  - 0021-9606
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  - Wirth, Jonas
A1  - Saalfrank, Peter
T1  - The chemistry of water on alpha-alumina kinetics and nuclear quantum effects from first principles
JF  - The journal of physical chemistry : C, Nanomaterials and interfaces
N2  - Water adsorption on an alumina (alpha-Al2O3) surface is studied here from first principles using periodic density functional theory in the generalized gradient approximation. Two different coverage regimes, low and high, are considered. For the low-coverage regime (with a coverage of 1/4 with respect to the number of coordinatively unsaturated Al sites), possible reactions at the surface such as dissociation, rotation, and diffusion of water and its fragments are investigated, using first principles thermodynamics and kinetics. A microkinetic model is set up with rates calculated from Eyring's transition state theory in order to cover a wide range of time scales. Special emphasis of this study is on the magnitude of quantum effects and on anharmonic corrections, particularly for reactions and dynamics. These have often been neglected in the past for water/alumina systems but can influence the system. This is particularly true for processes involving hydrogen atoms, where, for example, tunneling corrections to reaction rates are found to be important even at room temperature. For a higher-coverage regime (with a coverage of 2 ML), hydrogen dynamics becomes even more complex and is characterized, e.g., by concerted atom motion, strong anharmonicity, and delocalization. In this regime, classical molecular dynamics becomes questionable as well as quantum mechanical treatments based on the harmonic approximation.
Y1  - 2012
U6  - https://doi.org/10.1021/jp310234h
SN  - 1932-7447
VL  - 116
IS  - 51
SP  - 26829
EP  - 26840
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Schwarze, Thomas
A1  - Mickler, Wulfhard
A1  - Dosche, Carsten
A1  - Flehr, Roman
A1  - Klamroth, Tillmann
A1  - Löhmannsröben, Hans-Gerd
A1  - Saalfrank, Peter
A1  - Holdt, Hans-Jürgen
T1  - Systematic investigation of photoinduced electron transfer controlled by internal charge transfer and its consequences for selective PdCl2 coordination
N2  - Fluoroionophores of fluorophore-spacer-receptor format were prepared for detection of PdCl2 by fluorescence enhancement. The fluorophore probes 1-13 consist of a fluorophore group, in alkyl spacer and a dithiomaleonitrile PdCl2 receptor. First, varying the length of the alkylene spacer (compounds 1-3) revealed, dominant through-space pathway for oxidative photoinduced electron transfer (PET) in CH2-bridged dithiomaleonitrile fluoroionophores. Second. fluorescent probes 4-9 containing two anthracene or pyrene fragments connected through CH2 bridges to the dithiomaleonitrile unit were synthesized. Modulation of the oxidation potential (E-Ox) through electron-withdrawing or -donating groups on the anthracene moiety regulates file thermodynamic driving force for oxidative PET (Delta G(PET)) in bis(anthrylmethylthio)maleonitriles and therefore the fluorescence quantum yields (Phi(f)), too. The new concept was confirmed and transferred to pyrenyl ligands, and fluorescence enhancements (FE) greater than 3.2 in the presence of PdCl2 were achieved by 7 and 8 (FE=5.4 and 5.2). Finally, for comparison, monofluorophore ligands 10-13 were synthesized.
Y1  - 2010
UR  - http://onlinelibrary.wiley.com/doi/10.1002/chem.200902281/pdf
U6  - https://doi.org/10.1002/chem.200902281
SN  - 0947-6539
ER  - 
TY  - JOUR
A1  - Schwarze, Thomas
A1  - Mickler, Wulfhard
A1  - Dosche, Carsten
A1  - Flehr, Roman
A1  - Klamroth, Tillmann
A1  - Löhmannsröben, Hans-Gerd
A1  - Saalfrank, Peter
A1  - Holdt, Hans-Jürgen
T1  - Systematic investigation of photoinduced electron transfer controlled by internal charge transfer and its consequences for selective PdCl2 coordination
N2  - Fluoroionophores of fluorophore-spacer-receptor format were prepared for detection of PdCl2 by fluorescence enhancement. The fluorescent probes 1-13 consist of a fluorophore group, an alkyl spacer and a dithiomaleonitrile PdCl2 receptor. First, varying the length of the alkylene spacer (compounds 1-3) revealed a dominant through-space pathway for oxidative photoinduced electron transfer (PET) in CH2-bridged dithiomaleonitrile fluoroionophores. Second, fluorescent probes 4-9 containing two anthracene or pyrene fragments connected through CH2 bridges to the dithiomaleonitrile unit were synthesized. Modulation of the oxidation potential (EOx) through electron-withdrawing or -donating groups on the anthracene moiety regulates the thermodynamic driving force for oxidative PET (GPET) in bis(anthrylmethylthio)maleonitriles and therefore the fluorescence quantum yields (f), too. The new concept was confirmed and transferred to pyrenyl ligands, and fluorescence enhancements (FE) greater than 3.2 in the presence of PdCl2 were achieved by 7 and 8 (FE=5.4 and 5.2). Finally, for comparison, monofluorophore ligands 10-13 were synthesized.
Y1  - 2010
UR  - http://www3.interscience.wiley.com/journal/26293/home
SN  - 0947-6539
ER  - 
TY  - JOUR
A1  - Herder, Martin
A1  - Utecht, Manuel Martin
A1  - Manicke, Nicole
A1  - Grubert, Lutz
A1  - Pätzel, Michael
A1  - Saalfrank, Peter
A1  - Hecht, Stefan
T1  - Switching with orthogonal stimuli electrochemical ring-closure and photochemical ring-opening of bis(thiazolyl) maleimides
JF  - Chemical science
N2  - The photochemistry as well as electrochemistry of novel donor-acceptor bis(morpholinothiazolyl)maleimides has been investigated. Proper substitution of these diarylethene-type molecular switches leads to the unique situation in which their ring-closure can only be accomplished electrochemically, while ring-opening can only be achieved photochemically. Hence, these switches operate with orthogonal stimuli, i.e. redox potential and light, respectively. The switch system could be optimized by introducing trifluoromethyl groups at the reactive carbon atoms in order to avoid by-product formation during oxidative ring closure. Both photochemical and electrochemical pathways were investigated for methylated, trifluoromethylated, and nonsymmetrical bis(morpholinothiazolyl) maleimides as well as the bis(morpholinothiazolyl) cyclopentene reference compound. With the aid of the nonsymmetrical "mixed" derivative, the mechanism of electrochemically driven ring closure could be elucidated and seems to proceed via a dicationic intermediate generated by two-fold oxidation. All experimental work has been complemented by density functional theory that provides detailed insights into the thermodynamics of the ring-open and closed forms, the nature of their excited states, and the reactivity of their neutral as well as ionized species in different electronic configurations. The particular diarylethene systems described herein could serve in multifunctional (logic) devices operated by different stimuli (inputs) and may pave the way to converting light into electrical energy via photoinduced "pumping" of redox-active meta-stable states.
Y1  - 2013
U6  - https://doi.org/10.1039/c2sc21681g
SN  - 2041-6520
VL  - 4
IS  - 3
SP  - 1028
EP  - 1040
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Floss, Gereon
A1  - Granucci, Giovanni
A1  - Saalfrank, Peter
T1  - Surface hopping dynamics of direct trans -> cis photoswitching of an azobenzene derivative in constrained adsorbate geometries
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - With ongoing miniaturization of electronic devices, the need for individually addressable, switchable molecules arises. An example are azobenzenes on surfaces which have been shown to be switchable between trans and cis forms. Here, we examine the "direct" (rather than substrate-mediated) channel of the trans -> cis photoisomerization after pi pi* excitation of tetra-tert-butyl-azobenzene physisorbed on surfaces mimicking Au(111) and Bi(111), respectively. In spirit of the direct channel, the electronic structure of the surface is neglected, the latter merely acting as a rigid platform which weakly interacts with the molecule via Van-der-Waals forces. Starting from thermal ensembles which represent the trans-form, sudden excitations promote the molecules to pi pi*-excited states which are non-adiabatically coupled among themselves and to a n pi*-excited and the ground state, respectively. After excitation, relaxation to the ground state by internal conversion takes place, possibly accompanied by isomerization. The process is described here by "on the fly" semiclassical surface hopping dynamics in conjunction with a semiempirical Hamiltonian (AM1) and configuration-interaction type methods. It is found that steric constraints imposed by the substrate lead to reduced but non-vanishing, trans -> cis reaction yields and longer internal conversion times than for the isolated molecule. Implications for recent experiments for azobenzenes on surfaces are discussed.
KW  - AM1 calculations
KW  - bismuth
KW  - configuration interactions
KW  - excited states
KW  - gold
KW  - isomerisation
KW  - organic compounds
KW  - photochemistry
KW  - van der Waals forces
Y1  - 2012
U6  - https://doi.org/10.1063/1.4769087
SN  - 0021-9606
VL  - 137
IS  - 23
PB  - American Institute of Physics
CY  - Melville
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  - 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  - 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  - Füchsel, Gernot
A1  - Klamroth, Tillmann
A1  - Tremblay, Jean Christophe
A1  - Saalfrank, Peter
T1  - Stochastic approach to laser-induced ultrafast dynamics : the desorption of H-2/D-2 from Ru(0001)
N2  - The desorption of molecular hydrogen and deuterium induced by femtosecond-laser pulses is studied theoretically for the so-called DIMET (Desorption Induced by Multiple Electronic Transitions) process. These investigations are based on nonadiabatic classical Monte Carlo trajectory (CMCT) simulations on a ground and an excited state potential energy surface, including up to all six adsorbate degrees of freedom. The focus is on the hot-electron mediated energy transfer from the surface to the molecule and back, and the energy partitioning between the different degrees of freedom of the desorbing molecules. We first validate for a two-mode model comprising the desorption mode and the internal vibrational coordinate, the classical Monte Carlo trajectory method by comparing with Monte Carlo wavepacket (MCWP) calculations arising from a fully quantum mechanical open-system density matrix treatment. We then proceed by extending the CMCT calculations to include all six nuclear degrees of freedom of the desorbing molecule. This allows for a detailed comparison between theory and experiment concerning isotope effects, energy partitioning (translational, vibrational, and rotational energies and their distributions), and the dependence of these properties on the laser fluence. The most important findings are as follows. (i) CMCT agrees qualitative with the MCWP scheme. (ii) The basic experimental features such as the large isotope effect, the non-linear increase of yield with laser fluence, translationally hot products (in the order of several 1000 K) and non-equipartitioning of translational and internal energies (E-trans > E- vib > E-rot) are well reproduced. (iii) Predictions concerning a strong angular dependence of translational energies at large observation angles are also made.
Y1  - 2010
UR  - http://xlink.rsc.org/jumptojournal.cfm?journal_code=CP
U6  - https://doi.org/10.1039/C0cp00895h
SN  - 1463-9076
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  - Götze, Jan
A1  - Saalfrank, Peter
T1  - Serine in BLUF domains displays spectral importance in computational models
N2  - The BLUF (blue-light sensing using flavine) domain of the AppA photoreceptor protein from Rhodobacter sphaeroides was modelled by using quantum chemical chromophore plus amino acid models at the (TD-)B3LYP/6-31G* level of theory. The models were based on NMR structures, and further refined by CHARM force field molecular dynamics simulations. The goal is to explain the total redshift by about 10 nm in the UV/Vis spectra of BLUF domains after illumination, and to relate it to structural changes. For this purpose UV/Vis spectra of the available NMR structures were calculated and related to geometrical features. In particular, the hydrogen network embedding the central chromophore is discussed. Specifically, the position of a conserved glutamine, Q63, is found to be important in agreement with findings from previous works. Additionally, however, we find a systematic dependence also on the geometry of a conserved serine, S41. Based on a series of calculations with known structures and with artificial structural models, we argue that indeed the light-induced switching of both Q63 and S41 is necessary to explain the full similar to 10 nm redshift in the light (signalling) state of serine containing BLUF domains. Following or accompanying the double switching, two structurally highly important residues W104 and M106 exchange places, but do not affect the overall UV/ Vis properties of the chromophore.
Y1  - 2009
UR  - http://www.sciencedirect.com/science/journal/10111344
U6  - https://doi.org/10.1016/j.jphotobiol.2008.10.003
SN  - 1011-1344
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  - Tremblay, Jean Christophe
A1  - Saalfrank, Peter
T1  - Selective subsurface absorption of hydrogen in palladium using laser distillation
N2  - A theoretical model for the selective subsurface absorption of atomic hydrogen in a Pd(111) surface by infrared (IR) laser pulses is presented. The dynamics of the adsorbate is studied within the reduced density matrix approach. Energy and phase relaxation of the hydrogen atom are treated using the semigroup formalism. The vibrational excitation leading to subsurface absorption is performed using rationally designed pulses as well as IR laser pulses optimized on- the-fly. It is shown that dissipation can be used as a tool to transfer population to an otherwise inaccessible state via a mechanism known as "laser distillation." We demonstrate that when the reaction path is generalized from a reduced one-dimensional to full three-dimensional treatment of the system, the laser control strategy can prove very different.
Y1  - 2009
UR  - http://jcp.aip.org/
U6  - https://doi.org/10.1063/1.3212695
SN  - 0021-9606
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  - 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  - 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  - 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  - 
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  - 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  - Füchsel, Gernot
A1  - Tremblay, Jean Christophe
A1  - Klamroth, Tillmann
A1  - Saalfrank, Peter
T1  - Quantum dynamical simulations of the femtosecond-laser-induced ultrafast desorption of H2 and D2 from Ru(0001)
JF  - ChemPhysChem : a European journal of chemical physics and physical chemistry
N2  - We investigate the recombinative desorption of hydrogen and deuterium from a Ru(0001) surface initiated by femtosecond laser pulses. We adopt a quantum mechanical two-state model including three molecular degrees of freedom to describe the dynamics within the desorption induced by electronic transition (DIET) limit. The energy distributions as well as the state-resolved and ensemble properties of the desorbed molecules are analyzed in detail by using the time-energy method. Our results shed light on the experimentally observed 1) large isotopic effects regarding desorption yields and translational energies and 2) the nonequal energy partitioning into internal and translational modes. In particular, it is shown that a single temperature is sufficient to characterize the energy distributions for all degrees of freedom. Further, we confirm that quantization effects play an important role in the determination of the energy partitioning.
KW  - quantum dynamics
KW  - laser chemistry
KW  - isotope effects
KW  - surface chemistry
KW  - ultrafast reactions
Y1  - 2013
U6  - https://doi.org/10.1002/cphc.201200940
SN  - 1439-4235
VL  - 14
IS  - 7
SP  - 1471
EP  - 1478
PB  - Wiley-VCH
CY  - Weinheim
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  - 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  - Dokic, Jadranka
A1  - Gothe, Marcel
A1  - Wirth, Jonas
A1  - Peters, Maike V.
A1  - Schwarz, Jutta
A1  - Hecht, Stefan
A1  - Saalfrank, Peter
T1  - Quantum chemical investigation of thermal cis-to-trans isomerization of azobenzene derivatives : substituent effects, solvent effects, and comparison to experimental data
N2  - Quantum chemical calculations of various azobenzene (AB) derivatives have been carried out with the goal to describe the energetics and kinetics of their thermal cis -> trans isomerization. The effects of substituents, in particular their type, number, and positioning, on activation energies have been systematically studied with the ultimate goal to tailor the switching process. Trends observed for mono- and disubstituted species are discussed. A polarizable continuum model is used to study, in an approximate fashion, the cis -> trans isomerization of azobenzenes in solution. The nature of the transition state(s) and its dependence on substituents and the environment is discussed. In particular for push-pull azobenzenes, the reaction mechanism is found to change from inversion in nonpolar solvents to rotation in polar solvents. Concerning kinetics, calculations based on the Eyring transition state theory give usually reliable activation energies and enthalpies when compared to experimentally determined values. Also, trends in the resulting rate constants are correct. Other computed properties such as activation entropies and thus preexponential rate factors are in only moderate agreement with experiment.
Y1  - 2009
UR  - http://pubs.acs.org/journal/jpcafh
U6  - https://doi.org/10.1021/jp9021344
SN  - 1089-5639
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  - 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  - 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  - 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  - 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  - Schimka, Selina
A1  - Saalfrank, Peter
T1  - On the role of electronic friction for dissociative adsorption and scattering of hydrogen molecules at a Ru(0001) surface
JF  - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory
N2  - The role of electronic friction and, more generally, of nonadiabatic effects during dynamical processes at the gas/metal surface interface is still a matter of discussion. In particular, it is not clear if electronic nonadiabaticity has an effect under "mild" conditions, when molecules in low rovibrational states interact with a metal surface. In this paper, we investigate the role of electronic friction on the dissociative sticking and (inelastic) scattering of vibrationally and rotationally cold H-2 molecules at a Ru(0001) surface theoretically. For this purpose, classical molecular dynamics with electronic friction (MDEF) calculations are performed and compared to MD simulations without friction. The two H atoms move on a six-dimensional potential energy surface generated from gradient-corrected density functional theory (DFT), that is, all molecular degrees of freedom are accounted for. Electronic friction is included via atomic friction coefficients obtained from an embedded atom, free electron gas (FEG) model, with embedding densities taken from gradient-corrected DFT. We find that within this model, dissociative sticking probabilities as a function of impact kinetic energies and impact angles are hardly affected by nonadiabatic effects. If one accounts for a possibly enhanced electronic friction near the dissociation barrier, on the other hand, reduced sticking probabilities are observed, in particular, at high impact energies. Further, there is always an influence on inelastic scattering, in particular, as far as the translational and internal energy distribution of the reflected molecules is concerned. Additionally, our results shed light on the role played by the velocity distribution of the incident molecular beam for adsorption probabilities, where, in particular, at higher impact energies, large effects are found.
Y1  - 2013
U6  - https://doi.org/10.1021/jp403860p
SN  - 1089-5639
VL  - 117
IS  - 36
SP  - 8761
EP  - 8769
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  - Schmidt, Roland
A1  - Hagen, Sebastian
A1  - Brete, Daniel
A1  - Carley, Robert
A1  - Gahl, Cornelius
A1  - Dokic, Jadranka
A1  - Saalfrank, Peter
A1  - Hecht, Stefan
A1  - Tegeder, Petra
A1  - Weinelt, Martin
T1  - On the electronic and geometrical structure of the trans- and cis-isomer of tetra-tert-butyl-azobenzene on Au(111)
N2  - Near edge X-ray absorption. ne structure and X-ray photoelectron spectroscopy have been employed to follow the reversible trans to cis isomerization of tetra-tert-butyl-azobenzene (TBA) adsorbed on Au(111). For one monolayer the molecules adopt an adsorption geometry characteristic of the trans-TBA isomer. The azo-bridge (N = N) is aligned nearly parallel to the surface and the phenyl rings exhibit a planar orientation with a small tilt angle <= 4 degrees with respect to the surface normal. Illumination of the molecular layer at 455 nm triggers the trans to cis isomerization which is associated with a pronounced change of the geometrical and electronic structure. The N1s to pi* transition of the central azo-bridge shifts by 0.45 +/- 0.05 eV to higher photon energy and the transition dipole moment (TDM) is tilted by 59 +/- 5 degrees with respect to the surface normal. The pi-system of one phenyl ring is tilted by about 30 degrees with respect to the surface normal, while the second ring plane is oriented nearly perpendicular to the surface. This reorientation is supported by a shift and broadening of the C-H resonances associated with the tert-butyl legs of the molecule. These findings support a configuration of the photo-switched TBA molecule on Au(111) which is comparable to the cis-isomer of the free molecule. In the photo-stationary state 53 +/- 5% of the TBA molecules are switched to the cis configuration. Thermal activation induces the back reaction to trans-TBA.
Y1  - 2010
UR  - http://pubs.rsc.org/en/content/articlehtml/2010/cp/b924409c
U6  - https://doi.org/10.1039/B924409c
SN  - 1463-9076
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  - GEN
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
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 cm2 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.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 196 
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-81198
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  - 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 : PCCP ; 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 cm2 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  - 27
IS  - 17
SP  - 18079
EP  - 18086
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  - 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  - 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. <br /> 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  - 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  - 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  - Klinkusch, Stefan
A1  - Klamroth, Tillmann
A1  - Saalfrank, Peter
T1  - Long-range intermolecular charge transfer induced by laser pulses : an explicitly time-dependent configuration interaction approach
N2  - In this paper, we report simulations of laser-driven many-electron dynamics by means of the time-dependent configuration interaction singles (TD-CIS) approach. The method is capable of describing explicitly time-dependent phenomena beyond perturbation theory and is systematically improvable. In contrast to most time-dependent density functional methods it also allows us to treat long-range charge-transfer states properly. As an example, the laser-pulse induced charge transfer between a donor (ethylene) and an acceptor molecule (tetracyanoethylene, TCNE) is studied by means of TD-CIS. Also, larger aggregates consisting of several donors and/or acceptors are considered. It is shown that the charge distribution and hence the dipole moments of the systems under study are switchable by (a series of) laser pulses which induce selective, state-to-state electronic transitions.
Y1  - 2009
UR  - http://xlink.rsc.org/jumptojournal.cfm?journal_code=CP
U6  - https://doi.org/10.1039/B817873a
SN  - 1463-9076
ER  - 
TY  - JOUR
A1  - Klinkusch, Stefan
A1  - Saalfrank, Peter
A1  - Klamroth, Tillmann
T1  - Laser-induced electron dynamics including photoionization : a heuristic model within time-dependent configuration interaction theory
N2  - We report simulations of laser-pulse driven many-electron dynamics by means of a simple, heuristic extension of the time-dependent configuration interaction singles (TD-CIS) approach. The extension allows for the treatment of ionizing states as nonstationary states with a finite, energy-dependent lifetime to account for above-threshold ionization losses in laser-driven many-electron dynamics. The extended TD-CIS method is applied to the following specific examples: (i) state-to-state transitions in the LiCN molecule which correspond to intramolecular charge transfer, (ii) creation of electronic wave packets in LiCN including wave packet analysis by pump-probe spectroscopy, and, finally, (iii) the effect of ionization on the dynamic polarizability of H-2 when calculated nonperturbatively by TD-CIS.
Y1  - 2009
UR  - http://jcp.aip.org/
U6  - https://doi.org/10.1063/1.3218847
SN  - 0021-9606
ER  - 
TY  - JOUR
A1  - Saalfrank, Peter
A1  - Klamroth, Tillmann
A1  - Huber, C.
A1  - Krause, Pascal
T1  - Laser-driven electron dynamics at interfaces
N2  - In this paper we present time-dependent, quantum-dynamical simulations of photoinduced processes at solid surfaces involving nonadiabatic transitions of electrons to and from short-lived intermediate excited states. In particular, two-photon photoemission (2PPE) spectra of naked metal surfaces and free-standing metal films are considered. One major problem in both cases is the presence of electron-electron scattering, which is treated here in various ways. The first way is to adopt an open-system density matrix approach, in which a single electron is weakly coupled to a "bath" of other electrons. The second approach is based on a many-electron Schrodinger equation, which is solved with the help of a time-dependent configuration interactions singles (TD-CIS) method
Y1  - 2005
SN  - 0021-2148
ER  - 
TY  - JOUR
A1  - Klamroth, Tillmann
A1  - Kroner, Dominic
A1  - Saalfrank, Peter
T1  - Laser-driven coupled electron-nuclear dynamics : Quantum mechanical simulation of molecular photodesorption from metal films
N2  - In this paper we report dynamical simulations of laser-driven, coupled nuclear-electron dynamics for a molecule- surface system. Specifically, the laser desorption of a small molecule (NO) from a metal slab (Pt) in the so-called DIET limit (Desorption Induced by Electronic Transitions), is studied. The excitation of the metal electrons by a laser pulse followed by the formation of a negative ion resonance, its subsequent decay, and the simultaneous desorption of the molecule are all treated within a single quantum mechanical model. This model is based on an earlier theory of Harris and others [S. M. Harris, S. Holloway, and G. R. Darling, J. Chem. Phys. 102, 8235 (1995)], according to which a nuclear degree of freedom is coupled to an electronic one, both propagated on a single non-Born-Oppenheimer potential energy surface. The goals of the present contribution are (i) to make a conceptual connection of this model to the frequently adopted nonadiabatic "multi-state" models of photodesorption, (ii) to understand details of the desorption mechanism, (iii) to explicitly account for the laser pulse, and (iv) to study the photodesorption as a function of the thickness of the metal film, and the laser parameters. As an important methodological aspect we also present a highly efficient numerical scheme to propagate the wave packet in a problem-adapted diabatic basis
Y1  - 2005
SN  - 1098-0121
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  - 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  - 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  - 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  - 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  - 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  - 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  - JOUR
A1  - Vazhappilly, Tijo
A1  - Klamroth, Tillmann
A1  - Saalfrank, Peter
A1  - Hernandez, Rigoberto
T1  - Femtosecond-laser desorption of H-2 (D-2) from Ru(0001) : quantum and classical approaches
N2  - The femtosecond-laser-induced, substrate-mediated associative desorption of molecular hydrogen and deuterium from a Ru(0001) surface in the so-called DIMET limit is studied theoretically. Two widely used models, a "quantum nonadiabatic" approach and a "classical adiabatic" one are employed and compared to each other. The quantum model is realized by the Monte Carlo wave packet (MCWP) method in the framework of open-system density matrix theory: The classical approach is realized with the help of (frictional) Langevin dynamics with stochastic forces. For both models the same ground-state potential energy surface is used and the same two-temperature model adopted to describe the hot- electron-driven desorption dynamics. Apart from these common features both models are different. Still, both account well for the main experimental findings (Wagner et al. Phys. Rev. B 2005, 72, 205404). In particular, an isotope effect in desorption probabilities, the energy content of the desorbing molecules, and the scaling of these observables with laser fluence are reproduced and explained. The similarity of the results obtained with both models is traced back to the fact that, in the present case, the photodynamics takes place dominantly in the ground electronic state because the electronically excited state is rapidly quenched. The short lifetime of the excited state has also the effect that photoreaction cross sections are typically very small. An IR+vis hybrid scheme, by which the adsorbate is vibrationally excited by IR photons prior to the heating of metal electrons with the vis pulse, is shown to successfully promote the reaction even for strongly coupled adsorbate-surface systems.
Y1  - 2009
UR  - http://pubs.acs.org/journal/jpccck
U6  - https://doi.org/10.1021/Jp810709k
SN  - 1932-7447
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  - 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  - 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  - 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  - 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  - 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  - 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  - Tremblay, Jean Christophe
A1  - Monturet, Serge
A1  - Saalfrank, Peter
T1  - Electronic damping of anharmonic adsorbate vibrations at metallic surfaces
N2  - The nonadiabatic coupling of an adsorbate close to a metallic surface leads to electronic damping of adsorbate vibrations and line broadening in vibrational spectroscopy. Here, a perturbative treatment of the electronic contribution to the lifetime broadening serves as a building block for a new approach, in which anharmonic vibrational transition rates are calculated from a position-dependent coupling function. Different models for the coupling function will be tested, all related to embedding theory. The first two are models based on a scattering approach with (i) a jellium-type and (ii) a density functional theory based embedding density, respectively. In a third variant a further refined model is used for the embedding density, and a semiempirical approach is taken in which a scaling factor is chosen to match harmonic, single-site, first-principles transition rates, obtained from periodic density functional theory. For the example of hydrogen atoms on (adsorption) and below (subsurface absorption) a Pd(111) surface, lifetimes of and transition rates between vibrational levels are computed. The transition rates emerging from different models serve as input for the selective subsurface adsorption of hydrogen in palladium starting from an adsorption site, by using sequences of infrared laser pulses in a laser distillation scheme.
Y1  - 2010
UR  - http://prb.aps.org/
U6  - https://doi.org/10.1103/Physrevb.81.125408
SN  - 1098-0121
ER  - 
TY  - JOUR
A1  - Kopf, A.
A1  - Saalfrank, Peter
T1  - Electron transport through molecules treated by LCAO-MO Green's functions with absorbing boundaries
N2  - In this Letter, we present a method for calculating transport properties of molecular conductors using a time- independent scattering approach based on Green's functions with absorbing boundaries. The method, which has been used before for chemical reaction dynamics in a grid basis [Seideman, Miller, J. Chem. Phys. 96 (1992) 4412], is formulated here in an LCAO-MO form within simple Huckel theory and extended Huckel theory (EHT), respectively. Test calculations are for a quasi-one-dimensional atom chain. As a more realistic application, the organic molecules benzene- 1,4-dithiolate and biphenyl-4,4'-dithiolate between gold electrodes are studied. (C) 2004 Elsevier B.V. All rights reserved
Y1  - 2004
SN  - 0009-2614
ER  - 
TY  - JOUR
A1  - Nest, Mathias
A1  - Ludwig, M.
A1  - Ulusoy, I.
A1  - Klamroth, Tillmann
A1  - Saalfrank, Peter
T1  - Electron correlation dynamics in atoms and molecules
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - In this paper, we present quantum dynamical calculations on electron correlation dynamics in atoms and molecules using explicitly time-dependent ab initio configuration interaction theory. The goals are (i) to show that in which cases it is possible to switch off the electronic correlation by ultrashort laser pulses, and (ii) to understand the temporal evolution and the time scale on which it reappears. We characterize the appearance of correlation through electron-electron scattering when starting from an uncorrelated state, and we identify pathways for the preparation of a Hartree-Fock state from the correlated, true ground state. Exemplary results for noble gases, alkaline earth elements, and selected molecules are provided. For Mg we show that the uncorrelated state can be prepared using a shaped ultrashort laser pulse.
Y1  - 2013
U6  - https://doi.org/10.1063/1.4801867
SN  - 0021-9606
SN  - 1089-7690
VL  - 138
IS  - 16
PB  - American Institute of Physics
CY  - Melville
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  - 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  - 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  - 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  - 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  - 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  - 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  - Nacci, Christophe
A1  - Foelsch, Stefan
A1  - Zenichowski, Karl
A1  - Dokic, Jadranka
A1  - Klamroth, Tillmann
A1  - Saalfrank, Peter
T1  - Current versus temperature-induced switching in a single-molecule tunnel junction : 1,5 cyclooctadiene on Si(001)
N2  - The biconformational switching of single cyclooctadiene molecules chemisorbed on a Si(001) surface was explored by quantum chemical and quantum dynamical calculations and low-temperature scanning tunneling microscopy experiments. The calculations rationalize the experimentally observed switching driven by inelastic electron tunneling (IET) at 5 K. At higher temperatures, they predict a controllable crossover behavior between IET-driven and thermally activated switching, which is fully confirmed by experiment.
Y1  - 2009
UR  - http://pubs.acs.org/journal/nalefd
U6  - https://doi.org/10.1021/Nl901419g
SN  - 1530-6984
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  -