Dipolar Coupling and Molecular Vibrations in Crystals. II. Rhombohedral Lattices

Abstract

The Kornfeld–Ewald method of dipole summation in a lattice is applied to rhombohedral crystals with both unimolecular and bimolecular unit cells. These sums are evaluated as a function of the rhombohedral unit cell angle α. It is shown that the local field (Coulomb field) breaks into two parts, the macroscopic ε field and an “inner field” which is due to a transverse polarization wave. With the addition of the macroscopic ε field to the inner field the local field is that appropriate to a longitudinal polarization wave. The specific macroscopic shape dependence of the specimen implied by the use of the Kornfeld–Ewald method is discussed.