Non-adiabatic effects during the dissociative adsorption of O2 at Ag(111)? A first-principles divide and conquer study

TL;DR

This study uses first-principles calculations and neural network interpolation to analyze the dissociative adsorption of O2 on Ag(111), finding that high energy barriers explain low reactivity and that non-adiabatic effects are unlikely to be significant.

Contribution

It provides a detailed first-principles potential energy surface for O2 on Ag(111) and assesses the role of non-adiabatic effects in dissociation.

Findings

High energy barriers (>1.1 eV) limit O2 dissociation on Ag(111).

Adiabatic PES calculations match experimental low reactivity.

Non-adiabatic effects are unlikely to significantly influence dissociation probabilities.

Abstract

We study the gas-surface dynamics of O2 at Ag(111) with the particular objective to unravel whether electronic non-adiabatic effects are contributing to the experimentally established inertness of the surface with respect to oxygen uptake. We employ a first-principles divide and conquer approach based on an extensive density-functional theory mapping of the adiabatic potential energy surface (PES) along the six O2 molecular degrees of freedom. Neural networks are subsequently used to interpolate this grid data to a continuous representation. The low computational cost with which forces are available from this PES representation allows then for a sufficiently large number of molecular dynamics trajectories to quantitatively determine the very low initial dissociative sticking coefficient at this surface. Already these adiabatic calculations yield dissociation probabilities close to the scattered experimental data. Our analysis shows that this low reactivity is governed by large energy barriers in excess of 1.1 eV very close to the surface. Unfortunately, these adiabatic PES characteristics render the dissociative sticking a rather insensitive quantity with respect to a potential spin or charge non-adiabaticity in the O2-Ag(111) interaction. We correspondingly attribute the remaining deviations between the computed and measured dissociation probabilities primarily to unresolved experimental issues with respect to surface imperfections.