Graphene on Ni(111): Strong interaction and weak adsorption

The adsorption of graphene on Ni(111) has been investigated on the basis of the adiabatic-connection fluctuation-dissipation theorem in the random phase approximation (RPA). Although we find a significant hybridization between the graphene pi orbitals and Ni d(z)2 states at a binding distance of 2.17 angstrom, the adsorption energy is still in the range of a typical physisorption (67 meV per carbon). An important contribution to the energy is related to a decrease in the exchange energy resulting from the adsorption-induced lower symmetry in the graphene layer. The energetics can be well reproduced using the computationally significantly cheaper van der Waals density functional theory with an appropriately chosen exchange-correlation functional.