The one-phonon Green function and the dielectric properties of sodium chloride

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Abstract
The lowest order anharmonic contributions to the one-phonon Green functions for long wavelength phonons, and to the dielectric properties, have been calculated for sodium chloride. A breathing shell model was used to provide frequencies and eigenvectors. Coulomb contributions to the anharmonic matrix elements were included, and the volume dependence of all contributions was treated exactly. The phonon shifts and the static dielectric constant are in good agreement with experiment up to about three quarters of the melting temperature. The lowest order contribution to the width is about two thirds of the experimental value and, when the volume dependence is properly incorporated, varies with temperature as T1.6 in good agreement with experiment.