Structural, electronic, optical and elastic properties of layered rhombohedral compounds ALaSe₂(A=K, Rb): Insights from an <i>ab initio</i> study

Abstract

We report the results of first-principles calculations regarding the structural parameters, elastic moduli, electronic structure and optical properties of the ternary rhombohedral layered compounds, KLaSe 2 and RbLaSe 2 . These calculations were performed by employing the pseudo-potential plane-wave (PP-PW) method. Although the calculated structural parameters (a, c, V, c/a, bond-length d) using different exchange and correlation approximations are found in nice harmony with the available experimental data, the best agreement is obtained with the GGA-PW91 functional. The effect of the K–Rb substitution is noted very clearly on the degree of ionic bonding of the A–Se bond (A[Formula: see text]=[Formula: see text]K, Rb). The electronic band structure and the density of states (DoS) plots reveal the semiconducting characteristics of both compounds with an indirect bandgap energy, E[Formula: see text] of about 2 eV. The mechanical stability of the ALaSe 2 compounds is investigated for the first time by calculating the single-crystal elastic constants C[Formula: see text] using the stress-strain approach. In order to understand the linear optical properties of the studied systems, frequency-dependent polarized optical functions were computed for an energy range from 0.0 eV to 18 eV. Our calculated optical spectra reveal the isotropic nature of the optical properties of the ALaSe 2 compounds.