Theoretical Study of Structural, Electronic, Optical, and Elastic Properties of KLiX (X: S, Se, and Te) under Hydrostatic Pressure: A Pseudo Potential Plane Wave (PP-PW) Contribution

Abstract

We have studied structural, electronic, optical, and elastic properties of KLiX under pressure using the Density Functional Theory (DFT) within the Generalized Gradient Approximation (GGA) and the Local Density Approximation (LDA) for the exchange and correlation potential. The obtained structural results such as lattice parameters and internal sites of K atoms and chalcogenides are in good accordance with the available experimental and theoretical data. Band structure analysis shows that these compounds exhibit semiconductor properties with an indirect gap (Z → Г) for KLiS, KLiSe and direct gap (Г → Г) in the case of KLiTe using GGA, but in the use of LDA all compounds have an indirect energy gap (Z → Г) which take values 3.258 (3.455), 2.723 (2.810), and 2.441 (2.685) eV for KLiS, KLiSe, and KLiTe using GGA (LDA) respectively. These energy gap values decreased with increasing chalcogenide size (S → Se → Te). The combination of the states density and the charge density analysis confirms mixing of an ionic and a covalent chemical bonding character in the studied compounds. The optical properties such as the dielectric function, absorption coefficient, optical reflectivity, refractive index, extinction coefficient, and electron energy loss are calculated for radiation up to 12 eV. The elastic constants and their pressure dependence are calculated using the static finite strain technique.