AB-INITIO CALCULATION OF THE OPTICAL AND PHOTOELECTRON-SPECTRA OF KNBO3 AND KTAO3

The energy band structures of KNbO3 and KTaO3 cubic crystals have been calculated using the semi-relativistic Version of the self-consistent extended linear augmented plane wave method (ELAPW). The photoelectro n energy distribution curves (EDC) for h omega = 42 eV and optical spe ctra have been calculated within the local density approximation (LDA) . The EDCs are in good agreement with experiment. Deviations of the ca lculated optical spectra from the measured ones reveal the importance of the quasi-particle effects in the crystals studied. (C) 1997 Elsevi er Science B.V.