Charge-self-consistent LCAO band-structure calculations have been carried out for transition-metal compounds TiC, TiN, VC and VN and compared with experimental data. The effective atomic charges calculated self-consistently, employing the Mulliken population analysis, are used to study the charge transfer. The calculations have been used mainly to compare (i) the density of states with photoelectron spectra and (ii) the bands along Gamma -X with the available angle-resolved photoelectron spectroscopy data. In order to study the vacancy effect in these compounds, the same method was applied to a typical case of TiC0.75. The calculations account for the trends that are observed experimentally.
Charge self-consistent LCAO band structure (CSCBS) calculations are reported for orthorhombic YBazCu307 and tetragonal YBazCuaO~, assuming ordered vacancy models. The effective atomic charges are used to study the charge transfer. In YBa2Cu(1)1Cu(2)2OT, the two types of copper atoms have their energy bands almost overlapping with effective valency of each copper as 7/3 (or effective valency of each oxygen as approximately-13/7), so that electron hopping can take place without any loss or gain of energy while in YBa2Cu(1)~Cu(2)206, Cu(1) 1 is monovalent and Cu(2)2 are divalent with significant difference in their bands. Therefore, YBa2Cu307 should conduct much better compared to YBa2Cu30~. This corroborates the experimental observations that YBa2Cu3Ov is a (super)conductor while YBazCu306 is not. The calculated effective charges and DOS support the above view.
Preliminary results from our charge self-consistent LCAO band structure ( CSCsS) calculations with Bloch sums as the basis reveal that a noncorrosive reduced band gap electrode for photoelectrochemical solar cells may be produced from a ( 1: 1 ) mixture of p-Pb02 and Ti02 (both rutile). The band gaps for the constituents (p-Pb02 and TiOz) and the 1: 1 mixture are calculated and a detailed characterization of the valence and the conduction bands is undertaken to offer a possible mechanism for the reduction of the band gap of the mixture. The band gap for the perovskite PbTi03 is also calculated to offer a guideline for selecting from the competing pathways to the fabrication of noncorrosive photoelectrochemical electrodes.
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