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

The bonding and electronic structures of oxy-gen molecules adsorbed on Al (001) are theoretically investi-gated from first-principles using the density functional the-ory 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 con-sist 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 dif-ficult. 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 morpholo-gies.