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Thermodynamic, electronic, and optical properties of graphene oxide: a statistical ab initio approach
We study the incomplete oxidation of graphene or reduction of graphene oxide for hydroxyl and epoxy oxidant groups. While in wet oxidation hydroxyl groups are favorable, in a drier environment an oxygen atom can bridge two neighboring carbon atoms. We model composition variations and structural disorder within a statistical theory, the generalized quasichemical approximation, combined with density functional theory calculations of the local atomic geometries. A generalization of the statistical approach is developed to account for the antiparallel orientation of hydroxyl groups and a fourfold coordination of C atoms. The theoretical framework enables a thermodynamic treatment of graphene oxide as a function of oxygen content, allowing us to derive temperature-composition phase diagrams and investigate possible clustering and segregation. The resulting geometries, local and average electronic structures, and optical absorption spectra are discussed and compared with available experimental data.