TY - JOUR A1 - Tetenoire, Auguste A1 - Ehlert, Christopher A1 - Juaristi, Joseba Iñaki A1 - Saalfrank, Peter A1 - Alducin, Maite T1 - Why ultrafast photoinduced CO desorption dominates over oxidation on Ru(0001) JF - The journal of physical chemistry letters N2 - CO oxidation on Ru(0001) is a long-standing example of a reaction that, being thermally forbidden in ultrahigh vacuum, can be activated by femtosecond laser pulses. In spite of its relevance, the precise dynamics of the photoinduced oxidation process as well as the reasons behind the dominant role of the competing CO photodesorption remain unclear. Here we use ab initio molecular dynamics with electronic friction that account for the highly excited and nonequilibrated system created by the laser to investigate both reactions. Our simulations successfully reproduce the main experimental findings: the existence of photoinduced oxidation and desorption, the large desorption to oxidation branching ratio, and the changes in the O K-edge X-ray absorption spectra attributed to the initial stage of the oxidation process. Now, we are able to monitor in detail the ultrafast CO desorption and CO oxidation occurring in the highly excited system and to disentangle what causes the unexpected inertness to the otherwise energetically favored oxidation. Y1 - 2022 U6 - https://doi.org/10.1021/acs.jpclett.2c02327 SN - 1948-7185 VL - 13 IS - 36 SP - 8516 EP - 8521 PB - American Chemical Society CY - Washington, DC ER - TY - JOUR A1 - Choudhury, Arnab A1 - DeVine, Jessalyn A. A. A1 - Sinha, Shreya A1 - Lau, Jascha Alexander A1 - Kandratsenka, Alexander A1 - Schwarzer, Dirk A1 - Saalfrank, Peter A1 - Wodtke, Alec Michael T1 - Condensed-phase isomerization through tunnelling gateways JF - Nature : the international weekly journal of science N2 - Quantum mechanical tunnelling describes transmission of matter waves through a barrier with height larger than the energy of the wave(1). Tunnelling becomes important when the de Broglie wavelength of the particle exceeds the barrier thickness; because wavelength increases with decreasing mass, lighter particles tunnel more efficiently than heavier ones. However, there exist examples in condensed-phase chemistry where increasing mass leads to increased tunnelling rates(2). In contrast to the textbook approach, which considers transitions between continuum states, condensed-phase reactions involve transitions between bound states of reactants and products. Here this conceptual distinction is highlighted by experimental measurements of isotopologue-specific tunnelling rates for CO rotational isomerization at an NaCl surface(3,4), showing nonmonotonic mass dependence. A quantum rate theory of isomerization is developed wherein transitions between sub-barrier reactant and product states occur through interaction with the environment. Tunnelling is fastest for specific pairs of states (gateways), the quantum mechanical details of which lead to enhanced cross-barrier coupling; the energies of these gateways arise nonsystematically, giving an erratic mass dependence. Gateways also accelerate ground-state isomerization, acting as leaky holes through the reaction barrier. This simple model provides a way to account for tunnelling in condensed-phase chemistry, and indicates that heavy-atom tunnelling may be more important than typically assumed. Y1 - 2022 U6 - https://doi.org/10.1038/s41586-022-05451-0 SN - 0028-0836 SN - 1476-4687 VL - 612 IS - 7941 SP - 691 EP - 695 PB - Macmillan Publishers Limited, part of Springer Nature CY - London ER - TY - JOUR A1 - Kogikoski Junior, Sergio A1 - Tapio, Kosti A1 - Edler von Zander, Robert A1 - Saalfrank, Peter A1 - Bald, Ilko T1 - Raman enhancement of nanoparticle dimers self-assembled using DNA origami nanotriangles JF - Molecules : a journal of synthetic chemistry and natural product chemistry / Molecular Diversity Preservation International N2 - Surface-enhanced Raman scattering is a powerful approach to detect molecules at very low concentrations, even up to the single-molecule level. One important aspect of the materials used in such a technique is how much the signal is intensified, quantified by the enhancement factor (EF). Herein we obtained the EFs for gold nanoparticle dimers of 60 and 80 nm diameter, respectively, self-assembled using DNA origami nanotriangles. Cy5 and TAMRA were used as surface-enhanced Raman scattering (SERS) probes, which enable the observation of individual nanoparticles and dimers. EF distributions are determined at four distinct wavelengths based on the measurements of around 1000 individual dimer structures. The obtained results show that the EFs for the dimeric assemblies follow a log-normal distribution and are in the range of 10(6) at 633 nm and that the contribution of the molecular resonance effect to the EF is around 2, also showing that the plasmonic resonance is the main source of the observed signal. To support our studies, FDTD simulations of the nanoparticle's electromagnetic field enhancement has been carried out, as well as calculations of the resonance Raman spectra of the dyes using DFT. We observe a very close agreement between the experimental EF distribution and the simulated values. KW - surface-enhanced Raman scattering KW - DNA origami KW - resonance Raman KW - scattering KW - nanoparticle dimers Y1 - 2021 U6 - https://doi.org/10.3390/molecules26061684 SN - 1420-3049 VL - 26 IS - 6 PB - MDPI CY - Basel ER - TY - JOUR A1 - Witzorky, Christoph A1 - Paramonov, Guennaddi A1 - Bouakline, Foudhil A1 - Jaquet, Ralph A1 - Saalfrank, Peter A1 - Klamroth, Tillmann T1 - Gaussian-type orbital calculations for high harmonic generation in vibrating molecules BT - Benchmarks for H-2(+) JF - Journal of chemical theory and computation N2 - The response of the hydrogen molecular ion, H-2(+), to few-cycle laser pulses of different intensities is simulated. To treat the coupled electron-nuclear motion, we use adiabatic potentials computed with Gaussian-type basis sets together with a heuristic ionization model for the electron and a grid representation for the nuclei. Using this mixed-basis approach, the time-dependent Schrodinger equation is solved, either within the Born-Oppenheimer approximation or with nonadiabatic couplings included. The dipole response spectra are compared to all-grid-based solutions for the three-body problem, which we take as a reference to benchmark the Gaussian-type basis set approaches. Also, calculations employing the fixed-nuclei approximation are performed, to quantify effects due to nuclear motion. For low intensities and small ionization probabilities, we get excellent agreement of the dynamics using Gaussian-type basis sets with the all-grid solutions. Our investigations suggest that high harmonic generation (HHG) and high-frequency response, in general, can be reliably modeled using Gaussian-type basis sets for the electrons for not too high harmonics. Further, nuclear motion destroys electronic coherences in the response spectra even on the time scale of about 30 fs and affects HHG intensities, which reflect the electron dynamics occurring on the attosecond time scale. For the present system, non-Born-Oppenheimer effects are small. The Gaussian-based, nonadiabatically coupled, time-dependent multisurface approach to treat quantum electron-nuclear motion beyond the non-Born-Oppenheimer approximation can be easily extended to approximate wavefunction methods, such as time-dependent configuration interaction singles (TD-CIS), for systems where no benchmarks are available. KW - Basis sets KW - Chemical calculations KW - Ionization KW - Lasers KW - Quantum mechanics Y1 - 2021 U6 - https://doi.org/10.1021/acs.jctc.1c00837 SN - 1549-9618 SN - 1549-9626 VL - 17 IS - 12 SP - 7353 EP - 7365 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Rietze, Clemens A1 - Titov, Evgenii A1 - Granucci, Giovanni A1 - Saalfrank, Peter T1 - Surface hopping dynamics for azobenzene photoisomerization BT - effects of packing density on surfaces, fluorination, and excitation wavelength JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - Azobenzenes easily photoswitch in solution, while their photoisomerization at surfaces is often hindered. In recent work, it was demonstrated by nonadiabatic molecular dynamics with trajectory surface hopping [Titov et al., J. Phys. Chem. Lett. 2016, 7, 3591-3596] that the experimentally observed suppression of trans -> cis isomerization yields in azobenzenes in a densely packed SAM (self-assembled monolayer) [Gahl et al., J. Am. Chem. Soc. 2010, 132, 1831-1838] is dominated by steric hindrance. In the present work, we systematically study by ground-state Langevin and nonadiabatic surface hopping dynamics, the effects of decreasing packing density on (i) UV/vis absorption spectra, (ii) trans -> cis isomerization yields, and (iii) excited-state lifetimes of photoexcited azobenzene. Within the quantum mechanics/ molecular mechanics models adopted here, we find that above a packing density of similar to 3 molecules/nm(2), switching yields are strongly reduced, while at smaller packing densities, the "monomer limit" is quickly approached. The UV/vis absorption spectra, on the other hand, depend on packing density over a larger range (down to at least similar to 1 molecule/nm(2)). Trends for excited-state lifetimes are less obvious, but it is found that lifetimes of pi pi* excited states decay monotonically with decreasing coverage. Effects of fluorination of the switches are also discussed for single, free molecules. Fluorination leads to comparatively large trans -> cis yields, in combination with long pi pi* lifetimes. Furthermore, for selected systems, also the effects of n pi* excitation at longer excitation wavelengths have been studied, which is found to enhance trans -> cis yields for free molecules but can lead to an opposite behavior in densely packed SAMs. KW - Computational chemistry KW - Energy KW - Molecules KW - Monomers KW - Oligomers Y1 - 2020 U6 - https://doi.org/10.1021/acs.jpcc.0c08052 SN - 1932-7447 SN - 1932-7455 VL - 124 IS - 48 SP - 26287 EP - 26295 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Fischer, Eric W. A1 - Werther, Michael A1 - Bouakline, Foudhil A1 - Saalfrank, Peter T1 - A hierarchical effective mode approach to phonon-driven multilevel vibrational relaxation dynamics at surfaces JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistry N2 - We discuss an efficient Hierarchical Effective Mode (HEM) representation of a high-dimensional harmonic oscillator bath, which describes phonon-driven vibrational relaxation of an adsorbate-surface system, namely, deuterium adsorbed on Si(100). Starting from the original Hamiltonian of the adsorbate-surface system, the HEM representation is constructed via iterative orthogonal transformations, which are efficiently implemented with Householder matrices. The detailed description of the HEM representation and its construction are given in the second quantization representation. The hierarchical nature of this representation allows access to the exact quantum dynamics of the adsorbate-surface system over finite time intervals, controllable via the truncation order of the hierarchy. To study the convergence properties of the effective mode representation, we solve the time-dependent Schrodinger equation of the truncated system-bath HEM Hamiltonian, with the help of the multilayer extension of the Multiconfigurational Time-Dependent Hartree (ML-MCTDH) method. The results of the HEM representation are compared with those obtained with a quantum-mechanical tier-model. The convergence of the HEM representation with respect to the truncation order of the hierarchy is discussed for different initial conditions of the adsorbate-surface system. The combination of the HEM representation with the ML-MCTDH method provides information on the time evolution of the system (adsorbate) and multiple effective modes of the bath (surface). This permits insight into mechanisms of vibration-phonon coupling of the adsorbate-surface system, as well as inter-mode couplings of the effective bath. Y1 - 2020 U6 - https://doi.org/10.1063/5.0017716 SN - 0021-9606 SN - 1089-7690 VL - 153 IS - 6 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Penschke, Christopher A1 - Edler von Zander, Robert A1 - Beqiraj, Alkit A1 - Zehle, Anna A1 - Jahn, Nicolas A1 - Neumann, Rainer A1 - Saalfrank, Peter T1 - Water on porous, nitrogen-containing layered carbon materials BT - the performance of computational model chemistries JF - Physical chemistry, chemical physics : PCCP ; a journal of European chemical societies / RSC, Royal Society of Chemistry N2 - Porous, layered materials containing sp(2)-hybridized carbon and nitrogen atoms, offer through their tunable properties, a versatile route towards tailormade catalysts for electrochemistry and photochemistry. A key molecule interacting with these quasi two-dimensional materials (2DM) is water, and a photo(electro)chemical key reaction catalyzed by them, is water splitting into H-2 and O-2, with the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) as half reactions. The complexity of some C/N-based 2DM in contact with water raises special needs for their theoretical modelling, which in turn is needed for rational design of C/N-based catalysts. In this work, three classes of C/N-containing porous 2DM with varying pore sizes and C/N ratios, namely graphitic carbon nitride (g-C3N4), C2N, and poly(heptazine imides) (PHI), are studied with various computational methods. We elucidate the performance of different models and model chemistries (the combination of electronic structure method and basis set) for water and water fragment adsorption in the low-coverage regime. Further, properties related to the photo(electro)chemical activity like electrochemical overpotentials, band gaps, and optical excitation energies are in our focus. Specifically, periodic models will be tested vs. cluster models, and density functional theory (DFT) vs. wavefunction theory (WFT). This work serves as a basis for a systematic study of trends for the photo(electro)chemical activity of C/N-containing layered materials as a function of water content, pore size and density. Y1 - 2022 U6 - https://doi.org/10.1039/d2cp00657j SN - 1463-9076 SN - 1463-9084 VL - 24 IS - 24 SP - 14709 EP - 14726 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Fischer, Eric W. A1 - Saalfrank, Peter T1 - A thermofield-based multilayer multiconfigurational time-dependent Hartree approach to non-adiabatic quantum dynamics at finite temperature JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistry N2 - We introduce a thermofield-based formulation of the multilayer multiconfigurational time-dependent Hartree (MCTDH) method to study finite temperature effects on non-adiabatic quantum dynamics from a non-stochastic, wave function perspective. Our approach is based on the formal equivalence of bosonic many-body theory at zero temperature with a doubled number of degrees of freedom and the thermal quasi-particle representation of bosonic thermofield dynamics (TFD). This equivalence allows for a transfer of bosonic many-body MCTDH as introduced by Wang and Thoss to the finite temperature framework of thermal quasi-particle TFD. As an application, we study temperature effects on the ultrafast internal conversion dynamics in pyrazine. We show that finite temperature effects can be efficiently accounted for in the construction of multilayer expansions of thermofield states in the framework presented herein. Furthermore, we find our results to agree well with existing studies on the pyrazine model based on the pMCTDH method. Y1 - 2021 U6 - https://doi.org/10.1063/5.0064013 SN - 0021-9606 SN - 1089-7690 VL - 155 IS - 13 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Bedurke, Florian A1 - Klamroth, Tillmann A1 - Saalfrank, Peter T1 - Many-electron dynamics in laser-driven molecules BT - wavefunction theory vs. density functional theory JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - With recent experimental advances in laser-driven electron dynamics in polyatomic molecules, the need arises for their reliable theoretical modelling. Among efficient, yet fairly accurate methods for many-electron dynamics are Time-Dependent Configuration Interaction Singles (TD-CIS) (a Wave Function Theory (WFT) method), and Real-Time Time-Dependent Density Functional Theory (RT-TD-DFT), respectively. Here we compare TD-CIS combined with extended Atomic Orbital (AO) bases, TD-CIS/AO, with RT-TD-DFT in a grid representation of the Kohn-Sham orbitals, RT-TD-DFT/Grid. Possible ionization losses are treated by complex absorbing potentials in energy space (for TD-CIS/AO) or real space (for RT-TD-DFT), respectively. The comparison is made for two test cases: (i) state-to-state transitions using resonant lasers (pi-pulses), i.e., bound electron motion, and (ii) large-amplitude electron motion leading to High Harmonic Generation (HHG). Test systems are a H-2 molecule and cis- and trans-1,2-dichlorethene, C2H2Cl2, (DCE). From time-dependent electronic energies, dipole moments and from HHG spectra, the following observations are made: first, for bound state-to-state transitions enforced by pi-pulses, TD-CIS nicely accounts for the expected population inversion in contrast to RT-TD-DFT, in agreement with earlier findings. Secondly, when using laser pulses under non-resonant conditions, dipole moments and lower harmonics in HHG spectra are obtained by TD-CIS/AO which are in good agreement with those obtained with RT-TD-DFT/Grid. Deviations become larger for higher harmonics and at low laser intensities, i.e., for low-intensity HHG signals. We also carefully test effects of basis sets for TD-CIS/AO and grid size for RT-TD-DFT/Grid, different exchange-correlation functionals in RT-TD-DFT, and absorbing boundaries. Finally, for the present examples, TD-CIS/AO is observed to be at least an order of magnitude more computationally efficient than RT-TD-DFT/Grid. Y1 - 2021 U6 - https://doi.org/10.1039/d1cp01100f SN - 1463-9076 SN - 1463-9084 VL - 23 IS - 24 SP - 13544 EP - 13560 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Titov, Evgenii A1 - Sharma, Anjali A1 - Lomadze, Nino A1 - Saalfrank, Peter A1 - Santer, Svetlana A1 - Bekir, Marek T1 - Photoisomerization of an azobenzene-containing surfactant within a micelle JF - ChemPhotoChem N2 - Photosensitive azobenzene-containing surfactants have attracted great attention in past years because they offer a means to control soft-matter transformations with light. At concentrations higher than the critical micelle concentration (CMC), the surfactant molecules aggregate and form micelles, which leads to a slowdown of the photoinduced trans -> cis azobenzene isomerization. Here, we combine nonadiabatic dynamics simulations for the surfactant molecules embedded in the micelles with absorption spectroscopy measurements of micellar solutions to uncover the reasons responsible for the reaction slowdown. Our simulations reveal a decrease of isomerization quantum yields for molecules inside the micelles. We also observe a reduction of extinction coefficients upon micellization. These findings explain the deceleration of the trans -> cis switching in micelles of the azobenzene-containing surfactants. KW - azobenzene KW - micelles KW - photoswitches KW - rate constants KW - surfactants KW - surface hopping Y1 - 2021 U6 - https://doi.org/10.1002/cptc.202100103 SN - 2367-0932 VL - 5 IS - 10 SP - 926 EP - 932 PB - Wiley-VCH CY - Weinheim ER -