Ab initio density functional theory (DFT) was employed to study reconstructions of diamond (1 0 0) surfaces in the presence of hydrogen, oxygen and hydroxyl. Clean and (2 x 1): 1H surfaces are taken as reference. The properties of oxidization diamond surfaces with several adsorption structures, namely, O-on-top (OT) site, O-bridge (BR) site, hydroxyl (-OH), hydroxyl/hydroxyl, OT/hydroxyl, BR/hydroxyl have been considered. The calculated results indicate that the BR model is much more stable than the OT model, and the most energetically favorable structures of oxygenated surfaces are those with chemisorbed hydroxyl (-OH) group. Furthermore, the stability of the structures is also discussed from the point of HOMO-LUMO gap. Analysis of electronic structures shows that the presence of hydrogen induces surface conductivity whereas oxygen weakens it. (c) 2007 Elsevier B.V. All rights reserved.