Lattice dynamics of trigonal selenium. II. Model theories

Abstract

For pt.I see ibid., vol.8, p.3725 (1975). Phonon dispersion curves of trigonal selenium (Se) were studied using a valence force field model (VFFM) and a shell model (SM) with anisotropic core-shell coupling constants. The interchain coupling of the VFFM arises largely from forces representing interactions between adjacent bonds, suggesting covalent interchain bonding. Long range forces exist especially along the chains for the SM, which also gives correct values for the LO-TO splitting of the i.r. active A₂ and E₂ modes and the associated effective charges and also the low and high-frequency dielectric constants.