First-principles study of the structural, electronic, mechanical, and optical properties of Zintl-phase K2AgBi ternary compound for optoelectronic applications

A comprehensive first-principles study was conducted to explore the structural, electronic, mechanical, thermophysical, and optical properties of a Zintl-phase K2AgBi ternary semiconductor compound using density functional theory. The calculations employed the local density approximation (LDA), generalized gradient approximation (GGA), and meta-GGA methods. The computed negative formation energies proved the thermodynamic stability of the K2AgBi ternary compound. The computed bandgap values were 0.6732 and 0.7848 eV for the LDA and GGA, respectively. More refined bandgap estimates were obtained using meta-GGA methods, with the Tran–Blaha modified Becke–Johnson potential yielding 0.9346 eV and the revised strongly constrained and appropriately normed functional yielding 0.9778 eV. The projected density of states study revealed that the Ag3d, Bi2p, and K1s orbitals dominate the formation of the valence band, whereas the K4p, Ag2p, and K2s orbitals contribute significantly to the formation of the conduction band. Analysis of the mechanical properties confirmed that K2AgBi is mechanically stable and ductile. Optical analysis revealed strong absorption in the 1.0–15 eV energy range, high refractive index in the low-energy region, and distinct plasmonic response, suggesting potential applications in photovoltaics, optoelectronics, and plasmonic-based technologies.