First-principles and semiempirical calculations for bound-hole polarons inKNbO3

The ab initio linear muffin-tin-orbital formalism and the semiempirical met hod of the intermediate neglect of the differential overlap based on the Ha rtree-Fock formalism are combined for the study of the hole polarons (a hol e trapped nearby the cation vacancy) in a cubic phase of KNbO3 perovskite c rystals. The 40-atom and 320-atom supercells were used, respectively. We pr edict 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 exper imental data are discussed. [S0163-1829(99)12725-5].