A comprehensive study of the structural, elastic, electronic, and optical properties of the tetragonal sodium chalcogenides NaAlX2 (X = O, S, Se, Te).

We used first-principles electronic structure calculations to investigate the structural, elastic, electronic and optical properties of the already synthesised NaAlSe₂ and NaAlTe₂ tetragonal compounds and the predicted NaAlO₂ and NaAlS₂ tetragonal systems. The computed structural parameters using the GGA-PBE approach are consistent with the corresponding experimentally determined ones. The calculated single-crystal and polycrystalline elastic moduli show that the studied materials are mechanically stable and of a weak stiffness with strong elastic anisotropy. Calculated band structures reveal that NaAlO₂, NaAlS₂ and NaAlSe₂ are semiconductors with an indirect bandgap of Z-Γ type, while NaAlTe₂ is of a direct bandgap of Z-Z type. The calculated frequency-dependent linear optical functions show that the title compounds are characterised by significant optical anisotropy and high optical absorption for a wide photon energy range in the UV spectrum. [ABSTRACT FROM AUTHOR]