Mixed quantum-classical dynamics using collective electronic variables: A better alternative to electronic friction theories

TL;DR

This paper introduces a mixed quantum-classical method using collective electronic variables to improve the simulation of nonadiabatic dynamics on metallic surfaces, outperforming traditional electronic friction models.

Contribution

The authors develop a novel scheme that employs collective electronic variables via analytic block-diagonalization, offering a more accurate and robust alternative to existing electronic friction theories.

Findings

Collective-mode dynamics with few variables effectively describe various surface interactions.

The proposed method outperforms Ehrenfest and electronic friction models in simulations.

Electronic friction approaches can lead to unpredictable failures.

Abstract

An accurate description of nonadiabatic dynamics of molecular species on metallic surfaces poses a serious computational challenge associated with a multitude of closely-spaced electronic states. We propose a mixed quantum-classical scheme that addresses this challenge by introducing collective electronic variables. These variables are defined through analytic block-diagonalization applied to the time-dependent Hamiltonian matrix governing the electronic dynamics. We compare our scheme with the Ehrenfest approach and with a full-memory electronic friction model on a one-dimensional "adatom + atomic chain" model. Our simulations demonstrate that collective-mode dynamics with only few (2-3) electronic variables is robust and can describe a variety of situations: from a chemisorbed atom on an insulator to an atom on a metallic surface. Our molecular model also reveals that the friction approach is prone to unpredictable and catastrophic failures.