Accurate electronic band gap of pure and functionalized graphane from GW calculations

Using the GW approximation, we study the electronic structure of the recently synthesized hydrogenated graphene, named graphane. For both conformations, the minimum band gap is found to be direct at the $\ensuremath{\Gamma}$ point, and it has a value of 5.4 eV in the stable chair conformation, where H atoms attach C atoms alternatively on opposite sides of the two-dimensional carbon network. In the metastable boat conformation the energy gap is 4.9 eV. Then, using a supercell approach, the electronic structure of graphane was modified by introducing either a hydroxyl group or an H vacancy. In this last case, an impurity state appears at about 2 eV above the valence-band maximum.