Electronic Structure, Optical, and Elastic Properties of AgGaS2 Crystal: Theoretical Study

A comprehensive theoretical study of the structure, electronic, optical, and elastic properties of ternary semiconductor silver thiogallate crystal AgGaS₂ is carried out based on the density functional theory and dipole electron shifting model (DES) for finding a structure–properties relationship. The deformation and displacement parameters, describing the deviation of the structural parameters of AgGaS₂ from ideal chalcopyrite structure, are determined. It is noticed that the significant discrepancies concerning peculiarities of the band structure between initial results of the DFT-based calculation and the experiment for the titled crystal have been efficiently eliminated by choosing the proper DFT + U approach. By utilizing the calculated dielectric function for two principal directions, the refractive indices and extinction coefficients dispersions are determined. For the first time, the linear electro-optic properties, electrogyration coefficients, and second-order nonlinear optical coefficients of AgGaS₂ crystals are calculated in the frame of the DES model. The elastic properties of the AgGaS crystal are analyzed in the frame of the calculated full matrix of elastic coefficients. A number of parameters, such as Young's modulus E, Poisson's ratio ν, bulk B, and shear G moduli are predicted for the crystal. The calculated anisotropy coefficients for the moduli show very good agreement with ones available from experiment.