Ab-initio study of structural, elastic, electronic, Optical and Thermodynamic properties of sphalerite ZnS Compound

Abstract

This work presents an ab-initio investigation of the structural, elastic, electronic, optical, and thermodynamic properties of sphalerite ZnS under hydrostatic pressure using Density Functional Theory (DFT) within the plane-wave pseudopotential (PP-PW) method as implemented in CASTEP, employing the GGA-PBEsol approximation. The calculated results were analyzed and compared with available theoretical and experimental data. Increasing pressure up to 15 GPa leads to a continuous reduction in lattice constant and unit-cell volume. The elastic constants (C₁₁, C₁₂) and bulk modulus B increase with pressure, indicating enhanced mechanical stiffness. The compound preserves its direct band-gap nature at the Γ-point, while the band gap widens from 2.076 eV at 0 GPa to 2.716 eV at 15GPa. Optical spectra exhibit systematic variations in absorption coefficient, optical conductivity, and reflectivity under compression. Thermodynamic analysis (up to 15 GPa and 1000 K) shows a decrease in the thermal expansion coefficient and an increase in Debye temperature, whereas the heat capacity approaches the Dulong-Petit limit at high temperatures. These findings demonstrate the stability and pressure-tunable properties of sphalerite ZnS, highlighting its potential for advanced optoelectronic and high-pressure applications.