  The non-local van der Waals density functional (vdW-DF) approach is applied
to calculate the binding of graphene to Ir(111). The precise agreement of the
calculated mean height h = 3.41 {\AA} of the C atoms with their mean height h =
(3.38 \pm 0.04) {\AA} as measured by the X-ray standing wave (XSW) technique
provides a benchmark for the applicability of the non-local functional. We find
bonding of graphene to Ir(111) to be due to the van der Waals interaction with
an antibonding average contribution from chemical interaction. Despite its
globally repulsive character, in certain areas of the large graphene moir\'e
unit cell charge accumulation between Ir substrate and grapheneC atoms is
observed, signaling a weak covalent bond formation.
