A Critical Study of Dynamical Properties of Ionic Crystals

Abstract

AbstractThe basic differences among the three most popular extensions of the shell model i. e. the breathing shell model (BSM), the deformable shell model (DSM), and the three‐body force shell model (TSM) are sought out by applying their nearest‐neighbour versions to some representative rocksalt type ionic crystals. The phonon dispersion curves are determined by each model for each of the crystals and compared with the experimental phonons which forms perhaps the best test for this purpose. The same number (eight) of parameters of each model are determined by using the same set of input data. The results and degrees of agreement obtained in each case show clearly the superiority of the “charge‐transfer mechanism” for representing the deformations of electron shells, used in the TSM, over the “breathing” and “deformation mechanism” used in the BSM and DSM, respectively, for the same purpose. The study also shows that the TSM, DSM, and BSM form a series of descending order according to their relative degrees of agreement, obtained in explaining the lattice dynamical behaviour of these crystals.