Ab initio many-body study of cobalt adatoms adsorbed on graphene

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 the auxiliary-field quantum Monte Carlo method 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 sixfold 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 angstrom, corresponding to low-spin Co-2 (3d(9) 4s(0)) and high-spin Co-4 (3d(8) 4s(1)), respectively. DOI: 10.1103/PhysRevB.86.24140