Mechanical, thermal, electronic and optical properties of Cu₃NbS₄: an ab-initio study

In this work, mechanical, thermal, electronic and optical properties of Cu₃NbS₄ are evaluated by using density functional theory (DFT). The mechanical properties of Cu₃NbS₄ in the cubic phase are calculated by PBEsol approximation. By using calculated Young's modulus and shear modulus, with Poisson's ratio, conclude that the Cu₃NbS₄ structure is brittle material and also the 3D graphs of these parameters explained that the Cu₃NbS₄ behaves in a pseudo-symmetric manner. The calculated Debye temperature $\left({\theta }_D\right)$ for Cu₃NbS₄ is 429.2 K which allowed the use of the Debye-Gruneisen model to study the thermodynamic properties below this mention temperature. The amount of C_V and C_P of Cu₃NbS₄ at zero pressure and room temperature are studied and showed that these two curves cross each other, above 200 K. Furthermore, the electronic properties of Cu₃NbS₄ are studied and the results explain this structure has an indirect band gap in the zero temperature. The real part of the dielectric function and the static dielectric constant curves under different strain for Cu₃NbS₄ are investigated. The static dielectric constant decreases under tensile strain and increases under the compressive strain. The reflectivity under the different strains shows that the main peak shifted to higher energy (blue shift) under compressive strain and it shifted to lower energy (red shift) under tensile strain. Also, this compound shows strong optical absorption, with the absorption coefficient reaching 10⁶ cm⁻¹ that it has potential applications in solar cell industries. (paper)