  In extension of our previous study of KNbO_3 by the semiempirical
Hartree-Fock method we present parameterization and total-energy results for
non-ferroelectric KTaO_3 as a pure crystal (concentrating on the frozen phonon
calculations) and that with Li impurities. The magnitudes of off-center Li
displacements and the relaxation energies related to re-orientation of Li are
calculated and compared with experimental estimates and earlier calculation
results. The spatial extent of lattice relaxation around Li impurities and
contributions from different neighbors to the relaxation energy are discussed.
