First-principles and semiempirical calculations for bound-hole polarons in KNbO3

The ab initio linear muffin-tin-orbital formalism and the semiempirical method of the intermediate neglect of the differential overlap based on the Hartree-Fock formalism are combined for the study of the hole polarons (a hole trapped nearby the cation vacancy) in a cubic phase of KNbO3 perovskite crystals. The 40-atom and 320-atom supercells were used, respectively. We predict the existence of both one-site and two-site (molecular) polarons with close optical absorption energies (0.9 eV and 0.95 eV). The relevant experimental data are discussed. [S0163-1829(99)12725-5].