Determining the effect of hot electron dissipation on molecular scattering experiments at metal surfaces

TL;DR

This study uses advanced machine learning techniques to evaluate the accuracy of electronic friction theory in modeling hot electron effects during vibrational scattering of NO on Au(111), revealing its limitations and suggesting directions for improvement.

Contribution

It provides a comprehensive, quantitative assessment of electronic friction theory's performance in a key surface chemistry system using high-accuracy machine learning methods.

Findings

Electronic friction accurately predicts elastic and single-quantum energy loss.

It underestimates multi-quantum energy loss and overestimates trapping at high vibrational states.

Multi-quantum energy loss may be improved within friction theory, but trapping overestimation indicates a fundamental breakdown.

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 multi-quantum energy loss and overestimates molecular trapping at high vibrational excitation. Our analysis reveals that multi-quantum 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 require more sophisticated theories.