First-principles study of the electronic and optical properties of CuXS₂ (X = Al, Ga, In) and AgGaS₂ ternary compounds

First-principles calculations (using the CASTEP code, as implemented in the Materials Studio package) of electronic and optical properties of several representative ternary semiconductors (CuXS₂, X = Al, Ga, In, and AgGaS₂) were performed. After geometry optimization of the crystal structures, the band structures and partial and total densities of states were calculated and analyzed for all compounds considered. A scissor operator value of about 1.5eV was introduced systematically to overcome the intrinsic drawback of the calculation technique - underestimation of the calculated band gaps. From the dielectric functions calculated with this correction, Sellmeyer's approximations for the dependence of the refractive index on the wavelength were obtained for all crystals studied. The values of the refractive indices calculated are in reasonable agreement with the experimental data.