First-principles investigation of structural, electronic, optical, and thermoelectric properties of Li2X (X = Te, Se, S) chalcogenides for energy and optoelectronic applications

• Li 2 S is the most structurally stable among Li 2 X (X = S, Se, Te) compounds, confirmed by Birch-Murnaghan fitting. • Bandgaps decrease from Li 2 S (∼3.2 eV) to Li 2 Te (∼1.0 eV), with Li 2 Te suited for thermoelectrics, Li 2 Se for optoelectronics, and Li 2 S for solid-state electrolyte and optical uses • Li 2 Se is the stiffest and most ductile, while Li 2 Te and Li 2 S exhibit more elastic anisotropy. • Optical analysis shows increasing chalcogen mass enhances reflectivity and metallicity, indicating tunable electronic and energy device potential. The structural, electronic, optical, elastic, and thermoelectric properties of Li 2 X (X = S, Se, Te) chalcogenides were systematically investigated using density functional theory. Volume-energy analysis via Birch-Murnaghan fitting reveals that Li 2 S exhibits the greatest structural stability. The bandgaps decrease from Li 2 S (∼3.2 eV) to Li 2 Se (∼1.8 eV) and Li 2 Te (∼1.0 eV), correlating with lattice constants and chalcogen mass. Li 2 Te’s narrow direct bandgap and strong hybridization suggest thermoelectric potential, while Li 2 Se is promising for optoelectronics. Li 2 S, with a wide bandgap and high ionic conductivity, is ideal for optical and solid-state electrolyte applications. Elastic analysis shows Li 2 Se is the stiffest and most ductile, while Li 2 Te and Li 2 S show greater anisotropy. Optical results confirm that heavier chalcogens enhance reflectivity and metallicity, whereas lighter ones promote insulating behavior. These findings demonstrate the tunability of Li 2 X compounds for diverse energy and electronic applications.