First-principles calculation of the graphene Dirac band on semi-infinite Ir(111)

We study the energy dispersion relation of the pi and pi* bands in epitaxial monolayer graphene on a semi-infinite Ir(111) substrate by a first-principles density-functional calculation. For this purpose, we employ a realistic surface structure in which the (10x10) unit cell of graphene matches a (9 x 9) cell of Ir(111). We determine the surface geometry by using a slab model containing four pi layers, and the optimized structure is used as input for the subsequent surface embedded Green's function calculation. By taking advantage of semi-infinite calculations, we discuss mini energy gaps at the crossing of the pi band and its replicas, the Rashba-type spin splitting of the pi and pi* bands, and also the energy width of both bands arising from interactions with the energy continuum of bulk Jr bands.