DFT investigation of mechanical stability, optical response and high-temperature thermoelectric efficiency in cubic Cu ₂ Se

This study presents a comprehensive first-principles investigation of cubic Cu 2 Se, focusing on its structural, electronic, optical, elastic and thermoelectric properties using density functional theory (DFT). Structural optimization using LDA, PBE-GGA and PBEsol-GGA yields lattice constants of 5.663, 5.847 and 5.730 Å, respectively, with PBE-GGA providing the lowest ground-state energy and an equilibrium volume of 337.22 a.u. 3 . The calculated elastic constants ([Formula: see text] [Formula: see text] 97.23[Formula: see text]GPa, [Formula: see text] [Formula: see text]GPa and [Formula: see text] [Formula: see text] 58.03[Formula: see text]GPa) confirm mechanical stability and ductile behavior with a high Pugh’s ratio (B/[Formula: see text]) and strong elastic anisotropy ([Formula: see text]). Electronic structure analysis reveals semi-metallic behavior, with mBJ-GGA reducing the density of states at the Fermi level. Optical calculations show a high static dielectric constant ([Formula: see text]48 in GGA and [Formula: see text]17 in mBJ-GGA), strong ultraviolet absorption exceeding [Formula: see text] [Formula: see text]cm[Formula: see text], and a pronounced plasmon peak near 22 eV in the energy loss spectrum. Thermoelectric transport calculations predict a maximum figure of merit of ZT [Formula: see text] 0.28 at 1000[Formula: see text]K within the GGA framework, indicating the suitability of Cu 2 Se for mid-temperature thermoelectric applications.