First-principles investigation of structural, elastic, electronic, thermodynamic, and optical properties of KBi3 for optoelectronic applications.

KBi3, a recently explored non-layered cubic compound, offers a distinctive platform beyond conventional van der Waals-type materials due to its intriguing physical characteristics. In this study, we conduct a comprehensive first-principles density functional theory (DFT) investigation of its structural, elastic, electronic, thermodynamic, and optical properties to establish its potential for optoelectronic applications. The computed elastic constants satisfy Born stability criteria, and complementary mechanical indicators-including Pugh's ratio, Poisson's ratio, and Cauchy pressure-confirm the ductile and mechanically stable nature of KBi3. The electronic band structure and density of states demonstrate metallic behavior with finite states at the Fermi level, accompanied by anisotropic energy dispersion that reflects variation in carrier effective mass along different crystallographic directions. Thermodynamic analysis within the quasi-harmonic Debye model predicts a relatively low Debye temperature, moderate melting point, and reduced lattice thermal conductivity, suggesting limited heat transport. Meanwhile, the optical spectra reveal pronounced reflectivity in the infrared region, a high refractive index, and strong absorption spanning the visible-ultraviolet range, underscoring the compound's metallic character and multifunctional optical response. These findings provide the first detailed theoretical framework for KBi3 and highlight its promise as a candidate material for advanced optoelectronic device technologies.