Extended three-body-force shell-model dynamics of sodium-halide crystals

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Abstract
An extended three-body-force shell model has been developed for the lattice dynamics of ionic crystals by incorporating the effect of three-body and second-neighbor forces in the framework of the shell model with both ions polarizable. The versatility of the model has been tested by carrying out a qualitative analysis of the elastic and dielectric behavior of ionic crystals of rocksalt structure in general and a quantitative analysis of the phonon dispersion in sodium halides in particular. The model has been found to possess some remarkable features and describe more satisfactorily the dispersion of phonons in sodium halides as compared to those revealed by the original three-body-force shell model and other models.