We calculate the properties of a graphene monolayer on the Ir(111) surface, using the model in which the periodicities of the two structures are assumed equal, instead of the observed slight mismatch which leads to a large superperiodic unit cell. We use the Density Functional Theory approach supplemented by the recently developed vdW-DF nonlocal correlation functional. The latter is essential for treating the van der Waals interaction, which is crucial for the adsorption distances and energies of the rather weakly bound graphene. When additional iridium atoms are put on top of graphene, the electronic structure of C atoms acquires the sp3 character and strong bonds with the iridium atoms are formed. We discuss the validity of the approximations used, and the relevance for other graphene-metal systems.
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