DIPOLAR COUPLING AND MOLECULAR VIBRATIONS IN CRYSTALS .2. RHOMBOHEDRAL LATTICES

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 E field and an inner field" which is due to a transverse polarization wave. With the addition of the macroscopic E 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."