Adsorption of O2 on the CaO and SrO (1Â 0Â 0) surfaces: A first-principles study

► The bridge-top site for both the CaO and SrO (1 0 0) surfaces is the most favorable site for O2 adsorption, with predicted adsorption energies of 1.437 eV and 1.236 eV, respectively. ► Detailed analysis of density of states, Mullikan population and vibration frequency are performed. ► The calculated results imply the possible formation of a peroxo (O22−) when O2 is adsorbed with the bridge-top mode on both CaO and SrO (1 0 0) surfaces.