Semiempirical Hartree-Fock calculations for

In applying the semiempirical intermediate neglect of differential overlap (INDO) method based on the Hartree-Fock formalism to a cubic perovskite-based ferroelectric material (Formula presented), it was demonstrated that the accuracy of the method is sufficient for adequately describing the small energy differences related to the ferroelectric instability. The choice of INDO parameters has been done for a system containing Nb. Based on the parametrization proposed, the electronic structure, equilibrium ground-state structure of the orthorhombic and rhombohedral phases, and Γ-TO phonon frequencies in cubic and rhombohedral phases of (Formula presented) were calculated and found to be in good agreement with the experimental data and with the first-principles calculations available.