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 - 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 -