▎ 摘　　要

We used ab initio calculations based on density functional theory (DFT) to investigate the binding of atomic oxygen on graphene, considering adsorption structures with sizes varying from sub-nanometric clusters to infinite overlayers. From an extensive set of studied configurations of oxygen dimers, trimers and tetramers we demonstrated a strong tendency of adsorbates to form close-packed structures. In the high O coverage regime, corresponding to a C/O ratio of 2:1, we identified two very favorable structures with a distribution of O adatoms which enables both the hybridization of all C-2p(z) states from the graphene pi electron network with the O-2p states, as well as the minimization of the electrostatic repulsion between negatively charged O atoms attached to the same side of the graphene sheet. Using DFT results obtained for small clusters we constructed a simple model able to describe the energetics of the O islands with sizes beyond those that can be directly treated by first principles methods. (C) 2012 Elsevier Ltd. All rights reserved.