Theoretical studies of the adsorption and decomposition of nitrous oxide (N2O) on clean and partially oxidized Si(100) clusters were performed by means of the hybrid density functional theory method. N2O underwent physisorption on the clean surface and chemisorption on the surface modified by molecular oxygen. The difference is clearly explained by means of electron transfer analysis. N2O dissociated to form N-2 on surface dimers modified with O, and the activation energies in this process were small. (c) 2007 Published by Elsevier B.V.