AN OVERLAP REPULSIVE INTERACTION IN IONIC MOLECULES AND CRYSTALS

An overlap repulsive interaction in an interaction potential is used to describe the nature of ion-ion interaction in alkali halides in the molecular as well as crystalline states. The repulsive interaction comes from the knowledge of the effective electron density function F(r) which satisfies the Poisson equation NABLA-2-U(r) = F(r). A constant based on the valence electrons of two combining atoms is introduced and assumed to be characteristic for both the states. The different contributions related to polarization forces and Van der Waals interactions are investigated for these molecules. In the analysis of crystal binding, the contributions arising from the Van der Waals dispersion forces and the repulsive interactions operative between nearest neighbours as well as next nearest neighbours have also been taken into account. The results of various spectroscopic constants, cohesive energy and bulk modulus for 20 alkali halides compare well with the corresponding experimental data.