Semiempirical Hartree-Fock calculations for pure and Li-doped

In an extension of our previous study of (Formula presented) by the semiempirical Hartree-Fock method we present parametrization and total-energy results for nonferroelectric (Formula presented) 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 reorientation 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.