Predictive Modeling of Novel GaAgX2 (X = S, Se) Chalcogenides: First-principles Study of Electronic, Optical, and Thermoelectric Properties

The most prominent aspects of ternary-type chalcogenides are their tunable optical abilities and outstanding thermoelectric stability. Here the advanced density functional theory is used to examine the complicated interaction of the electronic structure, optical, thermodynamic, and thermoelectric properties of novel GaAgX2 (X = S, Se) chalcogenides. The total energies vs volume of the two materials were computed to formulate ground state characteristics. Both the materials confirmed to have direct band gap nature with an energy gap of 0.8 eV, and 2.2 eV, using TB-mBJ potential, respectively. As compared to GaAgS2, the crystal structure of GaAgSe2 have more covalent bonds that enlarged the covalency and results in wider energy gap of GaAgSe2 as compared to GaAgS2. For the negative value of epsilon 1(omega), these materials display metallic nature, resulting to show a total reflection of the incoming photons. The GaAgS2 displays better absorption than GaAgSe2 materials with higher energy photons. With a few high peaks of refractive index in (2.8-5.5) eV energy range, suggesting these materials appropriate to be used in optical devices. These materials have positive Seebeck coefficients and are confirmed to have a p-type nature. At ambient temperature, GaAgS2 has lower thermal conductivity than GaAgSe2.