BONDING IN PURE SOLIDS A DENSITY FUNCTIONAL APPROACH

Abstract

The understanding of the mode of bonding in different elements have begun in 1916 with the pioneering contribution of G.N.Lewis [ 1 ] ;,.He propounded the electronic theory of chemical bond by assuming that a single bond forms due to sharing of two electrons parti- cipating in the bond by two atoms. It was thus possible to distinguish between various modes of bonding - ionic bond, covalent bond co-ordinative bond etc. However, these concepts faced formidable difficulties with the advent of quantum mechanics. A molecule consists of an ensemble of nuclei exerting mutually repulsive forces. Their dispersion is prevented by the attractive forces brought to-bear by the electrons. Any two nuclei are always interacting with the entire electron cloud and it is not permitted to associate two particular electrons with a bond since the principle of indistinguishability leads to an antisymmetric wave function and imposes on all electrons the duty to play, on the average, the same role. However, it is possible to translate some of the classical concepts of bonding in terms of electron density which has characteristic forms for different types of bonding.