Comprehensive analysis of the structural, elastic, electronic, optical, and mechanical properties of orthorhombic CS(NH2)2 under pressure: A first-principles approach

Abstract

This study provides a comprehensive theoretical assessment of the orthorhombic compound CS(NH2)2, examining its properties under varying pressure conditions. Employing the ultrasonic plane wave pseudopotential technique, first-principles calculations were conducted within the density functional theory (DFT) framework using the Perdew–Burke–Ernzerhof (PBE) generalized gradient approximation (GGA) exchange-correlation functional. The study evaluates the compound's structural, elastic, electronic, optical, and mechanical properties. Simulations with hydrostatic pressure up to 20 GPa reveal changes in structural properties, elastic constants, and mechanical properties. The study estimates material brittleness and ductility based on Poisson's ratio and the B/G ratio. Elastic anisotropy is analyzed using various anisotropy indices. The compound exhibits a direct band gap along the (Z - Z) direction up to 2 GPa, transitioning to a direct band gap along the (U - Z) direction under higher pressures. Additionally, the band gap decreases from 3.817 eV to 2.38 eV as pressure increases from 0 GPa to 20 GPa. Optical properties are investigated by calculating dielectric functions, absorption coefficient, conductivity, reflectivity, and refractive indices for photon frequencies up to 40 eV. The HOMO-LUMO energy gap is estimated at approximately 5.548 eV. Hirshfeld surface analysis indicates significant contributions to crystal packing from interactions such as H···S/S···H (48%), H···H (35%), H···N/N···H (7.8%), and C···H/H···C (5.1%). This research presents the first quantitative theoretical prediction of the elastic, electronic, and optical properties of CS(NH2)2, contributing to our understanding of its behavior under pressure. Although experimental confirmation is required, these findings significantly advance the existing knowledge on the compound's properties and behavior under pressure.