An ab initio LMTO approach, and a semi-empirical quantum chemical INDO method, were used to make super-cell calculations concerning basic point defects: F-type centres and hole polarons bound to a cation vacancy in the partially covalent perovskite. The existence of both 1-site and 2-site (molecular) polarons, with close absorption energies (1eV) was predicted.

Computer Simulations of Defects in Perovskite KNbO3 Crystals. R.I.Eglitis, E.A.Kotomin, A.V.Postnikov, N.E.Christensen, M.A.Korotin, G.Borstel: Ferroelectrics, 1999, 229[1-4], 69-75