Solids

Abstract

The structure of crystals is generally described by assuming a potential energy Φ(r ₁... r _N ) which depends on the positions r ₁... r _N of the nuclei. This potential determines all the physical properties of the crystal. The crystal structure at zero temperature is determined by the minimum of the potential energy. Every atom sits at its lattice point *. The displacements from these ideal lattice positions by thermal motion or elastic deformation are usually very small as compared with the lattice parameter, the distance between nearest neighbours in the crystal. The interaction potentials decrease with the internuclear distance and are usually quite small except for relatively near neighbours in the crystal lattice.