Coupling Coefficients and Elastic Constants of Caesium Halides

Following Kellermann, the Brillouin zone of caesium chloride is divided into 10 × 10 × 10 equal regions. The coupling coefficients are calculated for 56 non‐equivalent points including the origin of the Brillouin zone, a correct enumeration of which points yields a total of 1,000 wave vectors or 12,000 coupling coefficients. Reststrahlen frequency is used in preference to compressibility in the evaluation of the constants of the repulsive part. A relation between the elastic constants and the second order coupling coefficients different from that of K ELLERMANN is used, and within the limitations of the model, the agreement between theory and experiment for the elastic constants is reasonable, and is very good for the compressiblility.