Estimation of photoelastic constants of ammonium halide crystals

A theoretical model for evaluating the photoelastic constants of ionic solids is developed by taking into account the long-range Coulombian, van der Waals and three-body interactions as well as the electronic polarizabilities of cations and anions. Hafemeister Flygare type short-range overlap repulsive potential effective upto nearest and next nearest neighbours is taken into account. The model is applied to calculate the photoelastic constants of ammonium halides with CsCl and NaCl type structures for the first time. The results obtained show a systematic trend in this group of solids. (author)