First-principles calculations of the elastic, electronic and optical properties of AgGaS2

Density functional theory calculations using ultrasoft pseudopotentials and the generalized gradient approximation were performed to investigate the elastic, electronic and optical properties of AgGaS2 crystals with chalcopyrite structure. The optimized structure parameters are in good agreement with the experimental data. The mechanical stability of AgGaS2 is confirmed by calculations of the elastic constants. The band structure and density of states were calculated and it is shown that the crystal is a semiconductor with a direct energy band gap of about 1.005 eV for AgGaS2. Calculations of the optical properties, namely the dielectric function, refractive index, extinction coefficient, absorption coefficient, optical reflectivity and electron energy loss spectrum, were performed for the energy range 0-25 eV. The results indicate that AgGaS2 is a promising mid-IR crystal material.