Comprehensive investigation of structural, electronic, optical, mechanical and thermoelectric properties of KCu₃SnSe₄ and RbCu₃SnSe₄: A density functional theory study

Quaternary chalcogenide materials have garnered significant attention due to their customizable structural, electronic and thermoelectric properties, making them suitable for diverse applications including thermoelectric devices and solar cells. This study investigates the structural, electronic, optical, mechanical and thermoelectric properties of KCu 3 SnSe 4 and RbCu 3 SnSe 4 via density functional theory (DFT). Structural analysis reveals stable crystalline configurations with RbCu 3 SnSe 4 demonstrating slightly higher equilibrium stability due to its larger ionic radius. Electronic properties exhibit semiconducting behavior, with direct band gaps influenced primarily by Cu-d and Se-p orbitals. Optical investigations indicate superior optical absorption and conductivity for RbCu 3 SnSe 4 . Mechanical characterization confirms both materials as ductile and elastically anisotropic, with moderate stiffness and good deformability. Thermal analyses illustrate superior thermoelectric performance for RbCu 3 SnSe 4 , achieving higher figure of merit (ZT) and Seebeck coefficients despite slightly higher thermal conductivity. These comprehensive insights underscore the potential of RbCu 3 SnSe 4 for optimized thermoelectric applications through strategic compositional tuning and doping.