▎ 摘　　要

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 (C(1)O). 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 C(1)O 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.