  We have systematically investigated the effect of oxidation on the structural
and electronic properties of graphene based on first-principles calculations.
Energetically favorable atomic configurations and building blocks are
identified, which contain epoxide and hydroxyl groups in close proximity with
each other. Different arrangements of these units yield an LDA band gap over a
range of a few eV. These results suggest the possibility of creating and tuning
the band gap in graphene by varying the oxidation level and the relative amount
of epoxide and hydroxyl functional groups on the surface.
