Semi-empirical INDO and shell-model calculations for perovskites

Structural, phonon and some elastic and dielectric properties have been cal culated for various paraelectric or ferroelectric phases of the perovskites KNbO3 and SrTiO3 using either the semi-empirical INDO (Intermediate Neglec t of Differential Overlap) method or a temperature-dependent shell model. T he INDO method was used to calculate the energy changes resulting from [100 ], [110] or [111] displacements of Nb atoms in the cubic perovskite cell of KNbO3 at OK. The conventional shell model gives a good account of the elas tic, dielectric and phonon properties of the cubic phase of strontium titan ate at room temperature, but difficulties remain in modelling the permittiv ity and elastic properties of KNbO3.