  Graphene oxide (GO) holds significant promise for electronic devices and
nanocomposite materials. A number of models were proposed for GO structure,
combining carboxyl, hydroxyl, carbonyl and epoxide groups at different
locations. The complexity and variety of GO isomers, whose thermodynamic
stability and formation kinetics depend on applied conditions, make
determination of GO structure with atomistic precision challenging. We report
high level theoretical investigation of multiple molecular configurations,
which are anticipated in GO. We conclude that all oxygen containing groups at
the GO surface are thermodynamically permitted, whereas the edge positions are
systematically more favorable than the center and side positions. We discuss a
potentially novel type of chemical bond or bonding reinforcement in GO, which
consists of a covalent bond and a strong electrostatic contribution from a
polarized graphene plane. We observe and analyze significant modifications of
graphene geometry and electronic structure upon oxidation. The reported
thermodynamic data guide experiments aimed at deciphering GO chemical
composition and structure, and form the basis for predicting GO properties
required for nano-technological applications.
