Calculations of two- and three-body dispersion coefficients for ions in crystals

Abstract

Coupled Hartree-Fock theory is used to calculate two and three body dispersion coefficients for in-crystal ions (Li⁺, Na⁺, K⁺, Rb⁺, Mg²⁺, Ca²⁺, F^-, Cl^-, O^2-) subject to both electrostatic and overlap interactions. For anions the reduction of the dispersion coefficients in the crystalline environment parallels the decrease of the static polarizability.

From comparison of ab initio results with those of the Slater-Kirkwood formula we propose an empirical scheme for calculating in-crystal dispersion coefficients from accurate static polarizabilities. We find that two-body dispersion forces are not responsible for the greater stability of the 8 : 8 compared to the 6 : 6 polymorph of CsCl.

A correlated Møller-Plesset calculation of the static polarizability of Rb⁺ confirms our previous scheme for deriving polarizabilities from experiment.