The adsorption and dissociation of O-2 on the perfect and oxygen-deficient Cu2O(1 1 1) surface have been systematically studied using periodic density functional calculations. Different kinds of possible modes of atomic O and molecular O-2 adsorbed on the Cu2O(1 1 1) surface are identified: atomic O is found to prefer threefold 3Cu site on the perfect surface and O-vacancy site on the deficient surface, respectively. Cu-CUS is the most advantageous site with molecularly adsorbed O-2 lying flatly over singly coordinate Cu-CUS-Cu-CSA bridge on the perfect surface. O-2 adsorbed dissociatively on the deficient surface, which is the main dissociation pathway of O2, and a small quantity of molecularly adsorbed O-2 has been obtained. Further, possible dissociation pathways of molecularly adsorbed O-2 on the Cu2O(1 1 1) surface are explored, the reaction energies and relevant barriers show that a small quantity of molecularly adsorbed O-2 dissociation into two O atoms on the deficient surface is favorable both thermodynamically and kinetically in comparison with the dissociation of O-2 on the perfect surface. The calculated results suggest that the presence of oxygen vacancy exhibits a strong chemical reactivity towards the dissociation of O-2 and can obviously improve the catalytic activity of Cu2O, which is in agreement with the experimental observation. (c) 2010 Elsevier B.V. All rights reserved.