Structural, electronic, optical and elastic properties of XLa2S4 (X = Ba; Ca): Ab initio study

XLa2S4 (X = Ba; Ca) sulfides are widely used as materials for application in infrared region, but the theoretical studies on these materials are limited and incomplete. Using the augmented plane wave + local orbitals (APW + lo) method with different approximation functionals, we performed a systematic theoretical study on the structural, electronic, optical and elastic properties of XLa2S4 (X = Ba; Ca). The calculated band gaps E-g of BaLa2S4 and CaLa2S4 using the modified Becke-Johnson potential in the form proposed by Tran and Blaha (TB-mBJ approximation) are 2.63 eV and 2.80 eV, respectively, which agree well with the experimental data. The dependence of main optical properties such as the absorption coefficient, refractive index, extinction coefficient, electron energy-loss spectrum, and optical reflectivity of BaLa2S4 and CaLa2S4 on photon energy were calculated and discussed. The independent elastic constants and elastic moduli of BaLa2S4 and CaLa2S4 were determined by precise calculations. The degree of elastic anisotropy of XLa2S4 (X = Ba; Ca) has been evaluated from 3D curved surface representations of Young's modulus. The results of the band structure and optical properties calculations suggest that XLa2S4 (X = Ba; Ca) are potential materials for solar conversion applications.