DFT study of the influence of Chalcogen substitution on the structural, mechanical, thermodynamic, magnetic, and electronic properties of Ag₃FeX₄ (X = S, Se, Te)

We investigated the structural, mechanical, and electronic properties of Ag₃FeX₄ (X = S, Se, Te) chalcogenides using density functional theory with PBE and PBE + U functionals. The compounds crystallize in a cubic P-43 m structure, showing systematic lattice expansion from 5.975 Å (S) to 6.423 Å (Te). Cohesive energy calculations reveal Ag₃FeS₄ as the most stable, with superior mechanical properties (bulk modulus = 22.87 GPa, shear modulus = 6.99 GPa), while Ag₃FeTe₄ exhibits greater ductility. Phonon dispersion confirms dynamical stability, with Debye temperatures decreasing from 149.3 K to 91.3 K, correlating with thermal conductivity variations. Magnetic properties demonstrate ferromagnetic ordering (∼3 μB) dominated by Fe 3d states, preserved under Hubbard U corrections. Electronic structure analysis shows metallic conductivity arising from Fe 3d-chalcogen p hybridization, unaffected by U corrections. The combination of metallic behavior, mechanical anisotropy, and thermal stability suggests potential applications in spintronics and thermoelectrics.