Ab-Initio investigation of the structural, electronic, mechanical, thermophysical, and optical properties of the Zintl-phase K₂AgSb ternary compound for optoelectronic applications

A Zintl-phase K₂AgSb ternary compound has been investigated using density functional theory (DFT) on its structural, electronic, mechanical, thermophysical, and optical properties. Various exchange-correlation functionals have been employed, including the local density approximation (LDA) and generalised gradient approximation (GGA). Regularised strongly constrained and appropriately normed (RSCAN) and Tran-Blaha modified Becke-Johnson (TB-mBJ) functionals were utilised to enhance the accuracy of electronic structure predictions. The computed band gap values were 1.1601 eV and 1.2559 eV using LDA and GGA approximations, respectively. In contrast, more refined estimates of 1.5274 eV and 1.8917 eV were obtained using the RSCAN and TB-mBJ functionals. Machine learning (ML) has been used to predict critical properties, such as band gaps and elastic moduli, and to guide the discovery of new materials with optimal performance. However, ML predicted the smallest band gap (0.94 eV), which may be due to limitations in the training data, systematic biases, or an inability to fully capture material-specific electronic structure corrections. The projected density of states (PDOS) analysis revealed that the K4 p , Ag2 p , and K2 s orbitals primarily contribute to the formation of the conduction band, whereas the Ag3d, Sb2p, and K1s orbitals dominate the valence band formation. Analysis of the mechanical properties confirmed that K₂AgSb is ductile with ionic bonding, which is a characteristic of Zintl-phase compounds. The optical properties demonstrated strong absorption within the ultraviolet - visible (1.0–15 eV) range, high refractive index, and a pronounced plasmonic response, highlighting its potential for optoelectronic and plasmonic technology applications. In addition, the reflectivity and energy loss spectra suggest the suitability of K₂AgSb for optical coatings and high-performance photonic devices.