ABSTRACT
The periodicity of the electronic density in crystals is a consequence of the translationally invariant symmetry of the atomic ordering. It is manifest in the solution, in terms of Bloch functions, for the many-electron problem in the presence of static nuclei. We shall see that nuclear vibrations, or phonons, introduce a further effective potential into the problem, and that this potential may tend to induce a periodicity into the electronic distribution that is distinct from that of the static-crystal symmetry. This result was first articulated by Fro¨hlich (1954). It had been presaged in work by Slater (1951) and was described qualitatively by Peierls in 1955. The approach of this chapter is based on a study by the present author [Vail (1964)] that examined the relationship between the Fermi level and charge-density-wave periodicity on the one hand, and stability of the charge density wave on the other.
