The interaction of molecular oxygen with the Cu(1 0 0) surface has been studied by using both Hartree-Fock and density functional methods in the framework of the cluster model approach. In this study, we have used the Cu-8(6,2) cluster in order to simulate the O-2 molecular adsorption on different high symmetry chemisorption sites (top-top, bridge-fourfold, bridge-cop, fourfold-fourfold) on the Cu(1 0 0) surface. High level non-local density functional (NLSD) computations indicate that the more stable chemisorption site is the bridge-bridge followed by the top-top, bridge-top and bridge-fourfold ones. The calculated 1s O XPS shifts are in good agreement with the experimental indications.