Computational insights into ternary bimetallic oxy-chalcogenides

Abstract

This study systematically investigates the optoelectronic properties of 36 ternary bimetallic compounds M(IB)M′(IIIA)X₂ (M = Ag, Au, Cu; M′ = Al, Ga, In; X = O, S, Se, Te) using density functional theory (DFT), with their thermodynamic and dynamical stability confirmed. Delafossite oxides are found to possess indirect band gaps, whereas chalcopyrite chalcogenides exhibit direct band gaps. Although both GGA and hybrid functionals predict qualitative trends in the band gaps, HSE06 provides a more reliable and quantitatively accurate description of the electronic structures, especially for compounds located near the semiconductor to semi-metal boundary. Specifically, HSE06 predicts monotonic band-gap narrowing with increasing atomic number, ranging from 3.85 eV for CuAlO₂ to 0.08 eV for AuInTe₂, thereby correcting the metallic character suggested by GGA. Several Au-based compounds are identified as semi-metallic under HSE06, due to substantially reduced band gaps and lowered conduction band minimum (CBM) energies, rather than true metallic behavior. SOC effect is almost negligible in oxides but becomes critical in Te-containing compounds. Optical calculations reveal low reflectivity and energy loss, along with strong absorption spanning the infrared to visible regions. Overall, these compounds exhibit finely tunable band gaps under hybrid-functional treatment, highlighting the necessity of beyond-GGA approaches for reliable materials screening. Their adjustable electronic and optical properties show significant, application-dependent potential across photon-active and electrode-related devices.