Interaction of dioxygen with Al clusters and Al(111): A comparative theoretical study

We have studied the interaction of an oxygen molecule with Al clusters and Al(111) using both wave-function-based quantum chemistry methods and density functional theory (DFT). These calculations were motivated by the fact that molecular beam experiments indicate that the adsorption Of O-2 on Al(111) should be activated whereas periodic DFT calculations yield purely attractive adsorption paths for almost all impact configurations Of O-2 on Al(111). On small Al-4 clusters, accurate wave-function-based quantum chemistry methods find a non-vanishing barrier in the O-2 adsorption. The DFT calculations for slabs and larger Al clusters confirm the important role of spin effects for the O-2 dissociation barrier on Al. The results indicate that exchange-correlation effects play a crucial role for the determination of the adsorption barrier in the O-2/Al system but their determination is hampered by serious technical problems that are discussed in detail.