Ab Initio Many-body Study of Cobalt Adatoms Adsorbed on Graphene

TL;DR

This study employs advanced quantum Monte Carlo methods to accurately determine the binding energies and electronic configurations of cobalt adatoms on graphene, revealing multiple stable states with nearly equal energies.

Contribution

It introduces a size-correction embedding scheme combined with AFQMC to precisely calculate Co-graphene binding energies, clarifying the nature of the bonding.

Findings

Three distinct ground states of Co on graphene identified.

Two binding states with nearly equal energies at different distances.

Different electronic configurations correspond to low-spin and high-spin states.

Abstract

Many recent calculations have been performed to study a Co atom adsorbed on graphene, with significantly varying results on the nature of the bonding. We use auxiliary-field quantum Monte Carlo (AFQMC) and a size-correction embedding scheme to accurately calculate the binding energy of Co on graphene. We find that as a function of the distance h between the Co atom and the six-fold hollow site, there are three distinct ground states corresponding to three electronic configurations of the Co atom. Two of these states provide binding and exhibit a double-well feature with nearly equal binding energy of 0.4 eV at h = 1.51 and h = 1.65 angstroms, corresponding to low-spin $^2$Co (3d9 4s0) and high-spin $^4$Co (3d8 4s1), respectively.