Selfconsistent band structures and optical calculations in cubic ferroelectric perovskites

Abstract

The band structures of SrTiO₃ BaTio₃ and KNbO₃ in the cubic perovsikte structure are calculated using the first-prinicipals selfconsistent orthogonalized linear combination of atomic orbitals method. In all three crystals, indirect band gaps of about 3 eV are obtained. The top of the valence band is at R and the minimum in the conduction band is at f. Effective charge calculation and the charg. 1 density maps reveal the highly ionic nature of the crystal bonding in these ferroelectric crystals. The optical conductivities and the frequency dependent dielectric functions up to 20 eV in all three crystals are also evaluated using the energy eigenvalues and wave functions obtained from the band calculation. The calculated spectra are found to be in good agreement with the existing experimental measurements.