Temperature dependence of the elastic constants of alkali halides

The pseudopotential theory of Ruffa has been used to calculate the temperature dependence of the elastic constants of alkali halides crystallizing in CsCl-like and NaCl-like structures, using the Lundquist potential, and taking the thermal expansion as the experimental input. This potential contains the many-body interactions, which explains the violation of Cauchy's relations even at 0^∘{}K. The agreement between these calculated results and the available experimental data is much better than that of any other recent theories. In the case of the NaCl-like structure, our present model for the first time predicts the anomalous increase in C₁₂ with temperature.