Crystal lattice dynamics of ZnGeP2 and AgGaS2 in hard ion model

A calculation is made of the long-wavelength phonon spectrum of ZnGeP₂ and AgGaS₂ in the hard ion model. The parameters of short-range forces and dynamic charges are found by comparing the theory with the experimental data on infrared absorption and Raman scattering of light. The elastic and piezoelectric constants are calculated. The available experimental data are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 3–10, May, 1980.