Theory of Dielectric Constants of LiF

The static and high-frequency dielectric constants and the effective charge of LiF are calculated on the basis of a simplified model in which the polarizability of the positive ion is neglected and that of the negative ion is attributed entirely to perturbations in the outermost subshell ($2p$) of electrons. The present calculation differs from the variational treatment of Yamashita mainly in the inclusion of perturbed wave functions differs from the variational treatment of Yamashita mainly in the inclusion of perturbed wave functions for the $2p$ electrons which are orthogonal to the core-electron wave functions. Also, different methods are employed in evaluating portions of the energy of the crystal in a field and in deducing the effective charge ratio e*e from the calculated energy. It is found that the use of trial wave functions which preserve the orthogonality within individual ions is of prime importance, and leads to results in generally better agreement with observation than the previously used nonorthogonal functions.