Electronic and optical properties of orthorhombic LiInS2 and LiInSe2: A density functional theory investigation

The structural, electronic and optical properties of two orthorhombic crystals, LiInS2 and LiInSe2, were calculated using the density functional theory. The optimized unit cells are in good agreement with experimental data. It is shown that the two crystals belong to the semiconductors with a direct energy band gap of about 3.17 eV for LiInS2 and 2.63 eV for LiInSe2. The important structural character of the two compounds is that there is a strong hybridization between In-5s, 5p orbits and S-3p (Se-4p) orbits at upper valence bands. The fundamental understanding on how the different anion (Se and S) affects the electronic and optical properties of the two crystals was highlighted in our calculations. The optical properties include the dielectric spectra, absorption, reflectivity and energy-loss spectra, and the origin of spectral peaks were analyzed based on the electronic structures. The results indicate that the two compounds are promising IR crystal materials.