Determining the Effect of Hot Electron Dissipation on Molecular Scattering Experiments at Metal Surfaces

Abstract

Nonadiabatic effects that arise from the concerted motion of electrons and atoms at comparable energy and time scales are omnipresent in thermal and light-driven chemistry at metal surfaces. Excited (hot) electrons can measurably affect molecule–metal reactions by contributing to state-dependent reaction probabilities. Vibrational state-to-state scattering of NO on Au(111) has been one of the most studied examples in this regard, providing a testing ground for developing various nonadiabatic theories. This system is often cited as the prime example for the failure of electronic friction theory, a very efficient model accounting for dissipative forces on metal-adsorbed molecules due to the creation of hot electrons in the metal. However, the exact failings compared to experiment and their origin from theory are not established for any system because dynamic properties are affected by many compounding simulation errors of which the quality of nonadiabatic treatment is just one. We use a high-dimensional machine learning representation of electronic structure theory to minimize errors that arise from quantum chemistry. This allows us to perform a comprehensive quantitative analysis of the performance of nonadiabatic molecular dynamics in describing vibrational state-to-state scattering of NO on Au(111) and compare directly to adiabatic results. We find that electronic friction theory accurately predicts elastic and single-quantum energy loss but underestimates multiquantum energy loss and overestimates molecular trapping at high vibrational excitation. Our analysis reveals that multiquantum energy loss can potentially be remedied within friction theory whereas the overestimation of trapping constitutes a genuine breakdown of electronic friction theory. Addressing this overestimation for dynamic processes in catalysis and surface chemistry will likely require more sophisticated theories

Perspective on integrating machine learning into computational chemistry and materials science

“…84,254,255 Similar progress has been achieved in nonadiabatic dynamics at metal surfaces, where NNs have been used to construct excited-state landscapes 4,256 and continuous representations of the electronic friction tensor 257 used in MD with electronic friction simulations. 258,259 Even full quantum dynamics simulations have recently seen an increasing uptake of ML methodology to push beyond longstanding limitations in the dimensionality of systems that can be simulated. The main bottleneck in quantum dynamics simulations is not the evaluation of the temporal evolution of the electrons, but the temporal evolution of the nuclear wavefunction, which involves computations that (formally) scale exponentially with the number of atoms in the system.…”

“…Going forward, complex dynamical simulation methods will become more accessible to nonexpert users with the help of ML and will open avenues to tackle complex systems in solvent environments 71 or dynamics at hybrid organic-inorganic interfaces. 259 It is evident that ML methods will play an important role in extending the range of applications for MQCD methods in the coming years. A recent work by Brieuc et al 277 employing ML methods to achieve converged path-integral MD simulations of reactive molecules in superfluid helium under cryogenic conditions is an exemplary showcase of what the synergy of ML and quantum dynamics methods can achieve.…”

Ab initio calculation of electron-phonon linewidths and molecular dynamics with electronic friction at metal surfaces with numeric atom-centered orbitals

“…[38] This implementation has enabled the calculation of on-the-fly MDEF simulations based on DFT for reactive scattering of H 2 on Ag(111) and has subsequently been used to construct machine-learning-based representations of the electronic friction tensor for state-to-state scattering of H 2 on Ag(111) [32,39,40] and NO on Au(111). [41] The electronic friction tensor can also be employed to directly calculate EPC-based vibrational linewidths equivalent to the conventional approach, by simply projecting the Cartesian friction tensor into normal mode space as shown in fig. 1, where ũqν refer to mass-weighted phonon displacement eigenmodes associated with phonon frequency ω qν .…”

Hot atom chemistry: oxygen at stepped platinum surfaces

“…From an experimental point of view this is due to the fact that the lifetime of dynamical hot atom events is typically so short that these events can not be directly detected. As far as simulations are concerned, in recent years significant progress has been made by performing dynamical simulations that include the coupling either to a phonon bath [15,[17][18][19][20][21] or to electron-hole pairs [22][23][24]. Such simulations have provided very valuable insights into hot atom dynamics in reactions Gambardella2001 at surfaces.…”