In this work, the structural, electronic structure and optical properties of CuXY2(X=In, Ga and Y=S, Se) chalcopyrite Semiconductors have been computed with density functional theory using numerical atomic orbital pseudopotential method with both local-density and generalized gradient approximations. The geometrical parameters like equilibrium lattice constant and anion displacement are in reasonable agreement with the experimental data and other theoretical results. Also electronic properties like band structures and density of states have been studied. The band structures show that CuXY2 compounds are semiconductors with a direct band gap and there is hybridization between Cu (d) with S (p) orbital in CuInS2 and CuGaS2 and hybridization between Cu (d) with Se (p) orbital in CuInSe2 and CuGaSe2. Furthermore, the optical properties, real part of the dielectric function, refractive index, reflectivity and absorption coefficients are calculated from the imaginary part of the dielectric function, which are compatible with the experimental data and earlier theoretical results.
