We have studied the interaction of an oxygen molecule with Al clusters and Al(111) using both wave-functionbased 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.

We performed total-energy calculations by the scalar-relativistic augmented-plane-wave method in the local-density and muffin-tin approximations for all 3d, 4d, and 5d transition metals in the fcc and bcc structures. These calculations predict the correct equilibrium structure and give good agreement with experiment and other calculations for lattice constants and bulk moduli.

Scalar relativistic self-consistent calculations of the band structure of Ne, Ar, Kr, and Xe have been performed with the augmented-plane-wave method using the Hedin-Lundqvist local-density (LD) expression for exchange and correlation. The trends with increasing atomic number in this inert-gas solid series are presented for the valence-band width, LD band gap, and for low-lying conduction-band eigenvalues. A simplified form of self-energy correction that accounts for dynamical exchange and correlation processes to the single-particle excitations is included. Comparisons are made with previous studies using diferent methods. The present approach is most reliable for valence-band properties and gives semiquantitative agreement with experimental values of the band-gap and conduction-band separations.

The oxidation states of Cu on the MgO(001) surface are studied using an ab initio cluster (five atoms plus charge array) calculation in the Hartree-Fock approximation, for two cases: (i) Cu above a surface oxygen and (ii) Cu in a surface Mg vacancy. Cu binds slightly atop oxygen with a binding energy comparable to room temperature. Above a Mg vacancy it binds strongly with binding energy of about 9 eV, and it stays stably at about 1 bohr above the surface as a Cu + ion: A Cu atom donates two electrons to empty antibonding surface orbitals of the surrounding surface oxygens. A Cu+ ion donates one electron to a similar surface orbital. A Cu + ion cannot stay stably in a Mg vacancy.