Lattice Dynamics

Abstract

The usual empirical classification of crystalline solids considers four types of materials: a) ionic; b) covalent; c) metallic and d) molecular crystals. This classification is based on differences in chemical and physical properties. As such the distinction among the various types of solids is not sharply defined. In fact the physical properties cover a continuous range of values and there are materials which are exactly in between the various categories of crystals. Nevertheless, the above classification is very convenient and in the present volume we shall be concerned primarily with the vibrational properties of the last type of crystals, the molecular crystals. It is, however, well understood that several aspects of both the experimental and the theoretical approach may be common to the various types of crystals.