Assessment of approaches for dispersive forces employing semihydrogenated graphene as a case study

Abstract

Abstract We study two interchange layer systems, (i) free standing semihydrogenated graphene, and (ii) semihydrogenated graphene on the Nickel (111) surface, to assess various density-functional-theory based computational schemes incorporating van der Waals forces. These various van der Waals methods range from semi-empirical force-field-like corrections, through non-local van der Waals density functionals, up to functionals involving exact exchange and the random phase approximation for correlation. Generally, all computational schemes lead to a similar qualitative picture of hydrogen-layer physisorption and chemisorption to graphene. The largest discrepancies between the approaches emerge for the energetics of the investigated systems. Our studies shed light on the physical mechanisms of graphene hydrogenation both in vacuum and in the proximity of a metallic surface. In particular, it is revealed that the adsorption of hydrogen atoms affects the nature of the bonding between graphene and the Ni(111) surface, from weak to strong semi-covalent bonding. On the other hand, it turns out that the adsorption of a hydrogen layer to graphene is stronger in the presence of the metallic surface.