Electronic, magnetic, optical, and thermoelectric properties of K₂OsCl₆ for spintronic and energy harvesting applications.

We report a comprehensive first-principles study of the structural, electronic, magnetic, optical, and thermoelectric properties of the double perovskite K2OsCl6 using density functional theory (DFT) within the generalized gradient approximation (GGA). The calculations predict a ferromagnetic ground state with a total magnetic moment of ~ 1.99 µB per formula unit, largely arising from Os atoms (~ 1.33 µB). Spin-resolved electronic band structures reveal robust half-metallicity, featuring a metallic majority-spin channel and a direct minority-spin band gap of ~ 0.8 eV, yielding nearly 100% spin polarization at the Fermi level. The optimized lattice constant of 10.45 Å shows excellent agreement with experimental data. Optical analysis demonstrates strong spin-dependent behavior in the visible and ultraviolet regions, with a peak absorption coefficient of ~ 1.5 × 105 cm⁻1 at 6 eV and static dielectric constants of 4.2 (spin-up) and 3.8 (spin-down). The refractive index exhibits anomalous dispersion, reaching refractive index values up to 2.8 in the visible range. Thermoelectric calculations indicate a Seebeck coefficient of ~ 180 µV/K at 900 K, electrical conductivity of 4.5 × 105 Ω⁻1 m⁻1, and low thermal conductivity of 2.8 W m⁻1 K⁻1 at room temperature.