Computer simulations of defects in perovskite KNbO3 crystals
  An ab initio LMTO approach and semi-empirical quantum chemical INDO method have been used for supercell calculations of basic point defects - F-type centers and hole polarons bound to cation vacancy - in partly covalent perovskite KNbO3. We predict the existence of both one-site and two-site (molecular) polarons with close absorption energies (~ 1 eV). The relevant experimental data are discussed and interpreted. 
R. I. Eglitis (1,2), E. A. Kotomin (2,3), A. V. Postnikov (3), N. E.   Christensen (4), M. A. Korotin (5), G. Borstel (3) ((...