ABSTRACT
Just as the properties of atoms are determined by their electronic configuration, we should expect that the properties of solids, which consist of spatial arrangements of atoms, reflect both the electronic structure of the separate atoms and the existing order in the atomic arrangements. An understanding of the solid is considerably simplified if it possesses a crystal structure characterized by a regular arrangement of identical structural units that each contains one or more atoms. Each of these units is called a basis and if the basis position is represented by a point in space, we obtain a periodic array of points called a lattice. Although the concept of a lattice only provides information about the geometry of the structure and has no physical reality, it provides a convenient frame for discovering the intrinsic regularities of the atomic arrangement in crystals. These regularities can lead to simplification of the physical models employed. The basis at each lattice point defines the atomic environment and allows the crystal structure to be built up by translation.
