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We have studied the pressure-induced structural phase transition and elastic constants at high pressures for four sodium halide crystals using a model potential that includes many-body interactions due to electron shell overlap. The present model potential has only one parameter, and other constants have been obtained from overlap integrals. The relative volume change at the phase transition for all four crystals shows a systematic trend of variation with anion-to-cation radius ratio, as is revealed from experiment. Previously reported theoretical results, however, fail to meet this essential criterion. The theoretically predicted phase-transition pressures and other structural properties for these solids agree reasonably well with the measured data. We could predict the shear instability to be around 35--50 GPa for all three halides except NaF, for which it is 65 GPa.
Rao et al. (Sun,) studied this question.