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We present dielectric-function-related optical properties such as absorption coefficient, refractive index, and reflectivity of the semiconducting chalcopyrites CuGaSe 2 and CuInSe 2 . The optical properties were calculated in the framework of density functional theory (DFT) using linear combination of atomic orbitals (LCAO) and full-potential linearized augmented plane wave (FP-LAPW) methods. The calculated spectral dependence of complex dielectric functions is interpreted in terms of interband transitions within energy bands of both chalcopyrites; for example, the lowest energy peak in the e 2 ðxÞ spectra for CuGaSe 2 corresponds to interband transitions from Ga/Se-4p fi Ga-4s while that for CuInSe 2 emerges as due to transition between Se-4p fi In-5s bands. The calculated dielectric constant, e 1 ð0Þ, for CuInSe 2 is higher than that of CuGaSe 2 . The electronic structure of both compounds is reasonably interpreted by the LCAO (DFT) method. The optical properties computed using the FP-LAPW model (with scissor correction) are close to the spectroscopic ellipsometry data available in the literature.

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