Evaluation of the First‐ and Higher‐Order Volume and Pressure Derivatives of Dielectric Constants of Alkali Halide Crystals

An analysis of first and higher order volume and pressure derivatives of low frequency or static dielectric constant is presented for sixteen alkali halide crystals with NaCl structure using seven different potential forms for the short range overlap repulsive energy. The potential parameters are calculated using recent values of van der Waals potentials and taking proper account of the thermal contribution derived from consistent experimental ultrasonic data. Calculated values of volume derivatives of dielectric constant and optic mode Grüneisen parameters are compared with available experimental data. The results obtained from some potential forms present distinctly better agreement with experiment in comparison of others. The usefulness of such potential forms is demonstrated in predicting the higher order pressure derivatives of dielectric constants of ionic crystals.