Variable-charge shell model for the lattice dynamics of thallous bromide

A variable-charge shell model has been used to calculate the dispersion curves of thallous bromide. This model yields as good a fit to the measured dispersion curves as the simple shell model of Cowley and Okazaki (see abstr. A37556 of 1967) using the same number of parameters, eleven, and it also yields a better fit to the Cauchy discrepancy and the high-frequency dielectric constant than Cowley and Okazaki's model.