Dipole-quadrupole dispersion coefficients for ions in crystals

Abstract

Ab initio coupled Hartree-Fock theory is used to compute dipolequadrupole C₈ dispersion coefficients for pairs of ions in crystals (LiF, LiCl and NaCl) and for inert gas atoms (He, Ne, Ar) interacting with these ions. Static quadrupole polarizabilities of Li⁺, Na⁺, F^- and Cl^- are also calculated. Coefficients involving anions are drastically reduced by electrostatic and overlap compression in the crystal, for the same reasons as the reduction of their static dipole and quadrupole polarizabilities. The approximate Starkschall-Gordon formula underestimates these coefficients by up to 30 per cent, even when applied in its optimal variant. The Starkschall-Gordon formula is tested further for inert gas pairs.