On the evaluation of the van der Waals potentials in ionic crystals

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Abstract
An application of the Slater–Kirkwood variational method has been made to evaluate the van der Waals dipole–dipole and dipole–quadrupole energies in the four families of ionic crystals, viz., alkali halides, alkaline earth chalcogenides, alkali chalcogenides, and alkaline earth halides. The methods based on the perturbation theory adopted by previous investigators to evaluate the van der Waals potentials are critically discussed. In the present paper we have used an interpolation scheme and semiempirical formulas to estimate the dipole–dipole and the dipole–quadrupole coefficients between a number of different ions with electron configurations close to those of the rare gas atoms. An independent check of the approximate validity of the interpolation scheme has been provided by evaluating the dipole–dipole interaction coefficients between alkali metal atoms. The crystal energies of alkali halides, calculated using the new values of van der Waals potentials, agree closely with the experimental values.