ABSTRACT
The problem of lattice dynamics in the harmonic approximation is to find the normal modes of a crystal. It is convenient to visualise an atom in a solid in terms of its ion core and valence electrons. The essential features of the lattice dynamics of crystals with a basis of more than one atom can be understood most simply by studying the dynamics of a diatomic linear chain, which can be viewed as a linear chain with a basis of two atoms. The rigid ion model, originally developed for the study of lattice dynamics of ionic crystals such as alkali halides, involves central pair interactions between the ions which are regarded as point charges. One of the most important quantities in lattice dynamical studies is the density of normal modes. The interatomic force constant method described for the one-dimensional case can be extended to calculate the normal modes of a general three-dimensional crystal.
