# Diffusion Monte Carlo Study of the O$_2$ Adsorption on a Single Layer Graphene

## TL;DR

This study uses diffusion Monte Carlo calculations to accurately analyze O₂ adsorption on single-layer graphene, revealing preferred orientations, adsorption sites, and diffusion barriers, with results aligning well with experimental data.

## Contribution

The paper provides the first DMC-based detailed characterization of O₂ adsorption sites, orientations, and energies on graphene, challenging previous DFT predictions.

## Key findings

- O₂ prefers a horizontal orientation at equilibrium distance.
- Midpoint of C-C bond (bridge site) is energetically favored for adsorption.
- O₂ diffusion barrier on graphene is approximately 11 meV.

## Abstract

Diffusion Monte Carlo (DMC) calculations were performed for an accurate description of the nature of the O$_2$ adsorption on a single layer graphene. We investigated the stable orientation of O$_2$ at a specific adsorption site as well as its equilibrium adsorption energy. At equilibrium adsorption distances, an O$_2$ molecule was found to prefer a horizontal orientation, where the O-O bond is parallel to the graphene surface, to the vertical orientation. However, the vertical orientation is favored at the O$_2$-graphene distances shorter than the equilibrium distance, which could be understood by the steric repulsion between O and C atoms. Contrary to previous DFT calculations, our DMC calculations show that the midpoint of a C-C bond (a bridge site) is energetically preferred for the O$_2$ adsorption to a center of a hexagonal ring (a hollow site). The lowest DMC adsorption energy was found at an intermediate point between a hollow and a bridge site, where the O$_2$ adsorption energy was estimated to be -0.142(4) eV that was in very good agreement with the recently-reported experimental value. Finally, we have found that O$_2$ is very diffusive on the surface of graphene with the diffusion barrier along a bridge-hollow-bridge path being as small as ~ 11 meV.