Structural motifs in oxidized graphene: A genetic algorithm study based on density functional theory

The structural and electronic properties of oxidized graphene are investigated on the basis of the genetic algorithm and density functional theory calculations. We find two new low-energy semiconducting phases of the fully oxidized graphene (C₁O). In one phase, there is parallel epoxy pair chains running along the zigzag direction. In contrast, the ground-state phase with a slightly lower energy and a much larger band gap contains epoxy groups in three different ways: normal epoxy, unzipped epoxy, and epoxy pair. Interestingly, the C₁O phase with the epoxy pair model has a lower conduction-band minimum than the Dirac point of graphene. For partially oxidized graphene, a phase separation between bare graphene and fully oxidized graphene is predicted.