  The ab initio linear muffin-tin-orbital (LMTO) formalism and the
semi-empirical method of the Intermediate Neglect of the Differential Overlap
(INDO) 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 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.
