First-principles studies of the adsorption of O2 on Al (001)

The bonding and electronic structures of oxygen molecules adsorbed on Al (001) are theoretically investigated from first-principles using the density functional theory within the generalization gradient approximation (GGA) and a supercell approach. The surface is described by means of a 2 × 2 cell with a thickness of fourteen layers, which consist of 9 layers of Al atoms and 5 layers of vacuum. Oxygen molecules are situated on Al surface. The calculated results indicate that oxygen molecules with their axes parallel to the Al surface are the energetically easiest to be adsorbed on Al (001), while those vertical to the Al surface are the most difficult. There are two different processes for the adsorption of oxygen molecules on Al (001), which are O2→(O2)2−→2O−→2O2− and O2→(O2)−→O2−+O, and their occurrences are strongly dependent on the initial morphologies.