We have calculated the electronic structure of the spin-dependent tunneling structures, Fe|Ge|Fe and Fe|GaAs|Fe, using first principles techniques. We find that there is a large charge transfer from the metal layer to the semiconductor layer; 0.21 electrons are transferred from Fe to Ge and 0.27 electrons are transferred from Fe to GaAs at each interface. The density of states of the interfacial metal layer is dramatically different from the other metal layers; there is a large peak in the density of states at the Fermi energy for the minority electrons. The electronic structure of the semiconductor layer is quite different for the majority and the minority spins although its total magnetic moment is negligible. Our results suggest that the theory of spin-dependent tunneling using the simple model of a potential barrier or a model based on densities of states taken from bulk band structures may not apply to these systems.

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A multiple scattering formulation for the electromigration wind force on atoms in dilute alloys is developed. The theory describes electromigration via a vacancy mechanism. The method is used to calculate the wind valence for electromigration in various host metals having a close-packed lattice structure, namely aluminum, the noble metals copper, silver, and gold, and the 4d transition metals. The self-electromigration results for aluminum and the noble metals compare well with experimental data. For the 4d metals small wind valences are found, which make these metals attractive candidates for the experimental study of the direct valence.

The reaction of H 2 S with chromium, chromia, and Au/chromia films grown on a Pt͑111͒ crystal has been investigated using synchrotron-based high-resolution photoemission spectroscopy. At 300 K, H 2 S completely decomposes on polycrystalline chromium producing a chemisorbed layer of S that attenuates the Cr 3d valence features. No evidence was found for the formation of CrS x species. The dissociation of H 2 S on Cr 3 O 4 and Cr 2 O 3 films at room temperature produces a decrease of 0.3-0.8 eV in the work function of the surface and significant binding-energy shifts ͑0.2-0.6 eV͒ in the Cr 3 p core levels and Cr 3d features in the valence region. The rate of dissociation of H 2 S increases following the sequence: Cr 2 O 3 ϽCr 3 O 4 ϽCr. For chromium, the density of states near the Fermi level is large, and these states offer a better match in energy for electron acceptor or donor interactions with the frontier orbitals of H 2 S than the valence and conduction bands of the chromium oxides. This leads to a large dissociation probability for H 2 S on the metal, and a low dissociation probability for the molecule on the oxides. In the case of Cr 3 O 4 and Cr 2 O 3 , there is a correlation between the size of the band gap in the oxide and its reactivity toward H 2 S. The uptake of sulfur by the oxides significantly increases when they are ''promoted'' with gold. The Au/Cr 2 O 3 surfaces exhibit a unique electronic structure in the valence region and a larger ability to dissociate H 2 S than polycrystalline Au or pure Cr 2 O 3 . The results of ab initio SCF calculations for the adsorption of H 2 S on AuCr 4 O 6 and AuCr 10 O 15 clusters show a shift of electrons from the gold toward the oxide unit that enhances the strength of the Au(6s)↔H 2 S(5a 1 ,2b 1 ) bonding interactions and facilitates the decomposition of the molecule.

A systematic study has been carried out on the electronic structure of YH3. The attention was focused on the conditions for finding an energy gap, in accordance with experimental evidence. The calculations are made with a localized spherical wave (LSW) program, which is based on a first-principles tight-binding version of the augmented spherical wave method. No gap was found for the FCC structure in spite of the use of a great variety of model parameters. However, a non-self-consistent run of the program for this structure reproduced the gap of 2 eV found by Switendick. No gap was found for several versions of the HCP structure either, including the rather complicated HoD3 structure. The separation of the bands around the Fermi level as found for the LaF3 structure, could explain the light transmission measurements.