Anisotropic Structural and Optical Properties of SnS Crystals: A Combined DFT and Hirshfeld Surface Analysis across Low Temperature Variations

This study investigates the anisotropic structural and optical properties of SnS crystals using Density Functional Theory (DFT) combined with Molecular Dynamics (MD) and Hirshfeld topological geometries (HTGs) analysis. The structural evolution of SnS under temperature variations from 5 K to 100 K reveals significant anisotropy, particularly along the c-axis. The lattice parameters at ambient pressure and temperature are a =4.329 Å, b =3.982 Å, c =11.18 Å, with the unit cell volume calculated as 192.72 Å 3 . The c-axis shows the most significant response, with a negative coefficient of linear expansion (-7.43 × 10-5 K-1), indicating contraction with rising temperature. Optical analyses reveal strong anisotropy, with the (001) plane exhibiting the highest reflectivity in the UV region. The electron localization function (ELF) demonstrates increasing electron delocalization with temperature, further affecting optical properties. These results verify the critical influence of the crystallographic c-axis on the structural stability and optical behavior of SnS crystal, particularly in temperature-sensitive optoelectronic applications.