Vibrational Relaxation at a Metal Surface: Electronic Friction Versus Classical Master Equations

TL;DR

This study compares electronic friction and classical master equations for vibrational relaxation of molecules at metal surfaces, revealing potential limitations of electronic friction and identifying optimal coupling conditions for relaxation.

Contribution

It introduces and compares three nonadiabatic dynamics schemes, including a new broadened classical master equation, for modeling vibrational relaxation at metal surfaces.

Findings

Electronic friction may produce spurious results in multi-dimensional scattering.

Optimal molecule-metal coupling enhances vibrational relaxation.

The broadened classical master equation interpolates between existing approaches.

Abstract

Within a 2-D scattering model, we investigate the vibrational relaxation of an idealized molecule colliding with a metal surface. Two perturbative nonadiabatic dynamics schemes are compared: $(i)$ electronic friction (EF) and $(ii)$ classical master equations (CME). In addition, we also study a third approach, $(iii)$ a broadened classical master equation (BCME) that interpolates between approaches $(i)$ and $(ii)$. Two conclusions emerge. First, even though we do not have exact data to compare against, we find there is strong evidence suggesting that EF results may be spurious for scattering problems with more than one nuclear dimension. Second, we find that there is an optimal molecule-metal coupling that maximizes vibrational relaxation rates by inducing large nonadiabatic interactions.