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 photoelectron energy distribution curves (EDC) for h omega = 42 eV and optical spectra have been calculated within the local density approximation (LDA). The EDCs are in good agreement with experiment. Deviations of the calculated optical spectra from the measured ones reveal the importance of the quasi-particle effects in the crystals studied. (C) 1997 Elsevier Science B.V.