Many Body Interaction in Alkali Halides

The effect of the many body interaction proposed by Sarkar and Sengupta is considered in detail. The method of homogeneous deformation is extended to include many body interactions in which the potential depends on several scaler distances. The general expressions for the elastic constants obtained by this method are compared with those obtained from the long wave theory. Including the various central interactions the model is applied to calculate the elastic constants, the cohesive energy, and the phase transition pressure for the six halides of potassium and rubidium. It is found that the inclusion of the three body interaction considerably improves the agreement.