Semi-empirical Hartree-Fock calculations for interacting Li impurities in KTaO3

Equilibrium off-center displacements of two Li impurities substituting neig hboring K sites in KTaO3, the relaxation pattern of O ions around the impur ities and the Li-Li interaction energies in fixed and relaxed O surrounding have been calculated using the semi-empirical INDO method. The Li off-cent er displacement is 0.6 - 0.7 Angstrom in all cases; the displacements of O nearest neighbors to Li are up to 0.06 Angstrom, and the displacement of mo re distant atoms negligibly small, within the calculational accuracy. The L i-Li interaction energy is positive, revealing the deviations from the dipo le-dipole interaction in a polarized crystal, and strongly enhanced due to the O relaxation.