ABINITIO BAND-STRUCTURE STUDIES OF BERYLLIUM AND BERYLLIUM-HYDROGEN ULTRATHIN FILMS

The electronic properties of hcp beryllium one-, two-, three-, and four-layer films and of a BeH2 monolayer have been reinvestigated by all-electron Hartree-Fock band-structure calculations with improved basis sets. In agreement with local-density-functional calculations, all Be layers are found to be metallic, in contrast with previous Hartree-Fock calculations, which predicted zero-band-gap semiconductors for the one-layer (1L), 2L, and 3L systems. The metallic character is due to the precursor of the Be(0001) 2p(z) surface state crossing the Fermi energy. However, this behavior is not observed for the BeH2 layer, which is still found to be insulating, contrary to local-density calculations, which predicted metallic behavior.