In order to understand various surface properties such as corrosion and potential catalytic activity of Cu2O surfaces in the presence of environmental gases, we report here spin-polarized density functional theory calculations of the adsorptions of atomic and molecular oxygen on three surface Cu2O facets. Atomic oxygen adsorbs at the hollow site formed with copper atoms of Cu2O(111), while its adsorption on the Cu2O(110) and Cu2O(100) induces surface reconstruction. Molecular oxygen adsorbs on one coordinated unsaturated surface copper atom and two coordinated saturated copper atoms of Cu2O(111), on the top of two surface copper atoms of Cu2O(110), and on four surface copper atoms on Cu2O(100). It was found that atomic O and molecular O-2 adsorption on the Cu2O(100) surface is stronger than on the Cu2O(111) surface. Atomic O and molecular O-2 adsorption on the surface of Cu2O(111) induces magnetism. This is different from other systems previously known to exhibit point defect ferromagnetism. On all three surfaces, dissociative adsorption was found to be energetically favorable. (C) 2014 Elsevier B.V. All rights reserved.