Ab-initio tensorial electronic friction for molecules on metal surfaces: nonadiabatic vibrational relaxation

TL;DR

This paper develops a tensorial electronic friction method based on Density Functional Theory to accurately model vibrational relaxation of molecules on metal surfaces, capturing nonadiabatic energy transfer effects.

Contribution

It introduces a numerically stable implementation of tensorial electronic friction using local atomic orbitals for condensed systems, enabling detailed vibrational relaxation studies.

Findings

Accurate vibrational relaxation rates for diatomic molecules on metal surfaces.

Identification of mode-coupling effects in CO adsorbates on Cu(100).

Benchmarking shows robustness and convergence of the method.

Abstract

Molecular adsorbates on metal surfaces exchange energy with substrate phonons and low-lying electron-hole pair excitations. In the limit of weak coupling, electron-hole pair excitations can be seen as exerting frictional forces on adsorbates that enhance energy transfer and facilitate vibrational relaxation or hot-electron mediated chemistry. We have recently reported on the relevance of tensorial properties of electronic friction [Phys. Rev. Lett. 116, 217601 (2016)] in dynamics at surfaces. Here we present the underlying implementation of tensorial electronic friction based on Kohn-Sham Density Functional Theory for condensed phase and cluster systems. Using local atomic-orbital basis sets, we calculate nonadiabatic coupling matrix elements and evaluate the full electronic friction tensor in the classical limit. Our approach is numerically stable and robust as shown by a detailed convergence analysis. We furthermore benchmark the accuracy of our approach by calculation of vibrational relaxation rates and lifetimes for a number of diatomic molecules at metal surfaces. We find friction-induced mode-coupling between neighboring CO adsorbates on Cu(100) in a c(2x2) overlayer to be important to understand experimental findings.