Configurational Model of Solids

Abstract

Two theories of the electron structure of crystals, the band theory of Bloch and the Heitler-London theory (also known as the Heitler-London-Heisenberg model), provide satisfactory explanations of most of the relationships governing the properties of solids with relatively simple electron structures [8–32]. However, these theories fail to account properly for the experimentally determined properties of d-type transition metals, whose atoms have partly filled inner shells in the free state, and of compounds of these metals. This is due to the complex electron structure of the substances with heterodesmic bonding. Therefore, it is necessary to review critically the assumptions and the approximations on which these simple theories are based. Since the effects which are not explained by these theories are important also in the limiting cases of alkali metals or dielectrics [33–35], we may conclude that these effects are important in the electron structure of all crystalline substances.