An extended three-body force shell model for the lattice-dynamics of ionic crystals

Abstract

An extended three-body force shell model (e. t. s. m.) for the dynamics of ionic crystals of cesium chloride structure has been developed by reformulating the original t. s. m. The dynamical matrix of the model consists of the long-range Coulomb and three-body interactions and short-range overlap repulsions effective up to the second-neighbours. The off-diagonal elements of this matrix along symmetry directions contain a completely new term having significant contribution for unequal shell charges. The long-wave aspects of e. t. s. m. have been explored to describe the elastic and dielectric behaviour of the crystals. The adequacy of e. t. s. m. to describe the lattice dynamics has been investigated by applying it to the case of thallous bromide (TIBr). The overall agreement between theoretical and experimental results seems to be encouraging and gives some confidence to regard it as an appropriate model for the dynamical description of ionic crystals.

van der Waals three-body force shell model (VTSM) for the lattice dynamical studies of thallous bromide

“…From the above discussion, our model provides good agreement between theory and experiment and is certainly better than those yielded by other works [4][5][6][7][8]. Therefore, it may be concluded that the inclusion of VWI is very essential for the complete description of the phonon dynamical behaviour of crystals with CsCl structure.…”

“…X, M and R for both the branches (optical as well as acoustic). Quantitatively, the agreement achieved from our present model is comparatively better in the sense that some of the fitted parameters by other workers [4][5][6][7][8] have attained unrealistic values. Moreover, we have tested the adequacy of the present model by calculating the Debye temperature variations, two phonon Raman and anharmonic elastic properties.…”

“…The phonon dynamics of ionic crystals with cesium chloride (CsCl) structure has been a subject of great interest in solid-state physics over the past four decades. The details of progression for the study of phonon behaviour of thallous bromide (TlBr) have been traced by several experimental [1][2][3] and theoretical works [4][5][6][7][8]. The subject has so far been extensively investigated by several theoretical models, which have progressed through simple phenomenological approaches to sophisticated microscopic approaches.…”