Molecular orbital studies of ABO3perovskites by the SCF-MS-Xα method: local densities of states, chemical bonding and optical transitions

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Abstract
The evolution of electronic properties for the series of perovskite compounds BaTiO3, KNbO3 and KTaO3 is investigated through the SCF-MS-X alpha method applied to TiO68-, NbO67- and TaO67- octahedral clusters. Local densities of states of d and p character are derived from X alpha ground states eigenvalues and compared with band energy results. Theoretical densities of states obtained when introducing photoionisation cross section effects are discussed in regard to XPS O 2p valence bands. Ionisation energies and optical transitions are calculated using the transition-state model and compared with XPS binding energies and experimental optical data, respectively. The spatial distributions of the molecular orbital and the characteristics of covalency deduced from a population analysis show slight variations along the series.