Spin polarized first principles study of electro-magnetic and optical properties of K2NaXI6 (X :Cr Fe) double halide perovskites

Spin-polarized first-principles calculations were performed to investigate the physical properties of K₂NaXI₆ (X = Cr, Fe) halide double perovskites. Accurate electronic band gaps were obtained using the TB-mBJ exchange potential. Ab initio molecular dynamics simulations confirm the thermodynamic stability of both compounds. Electronic structure analysis reveals semiconducting behavior in both spin channels for K₂NaCrI₆ and K₂NaFeI₆. The calculated band gaps for K₂NaCrI₆ are 0.8 eV in the spin-up channel and 1.8 eV in the spin-down channel, whereas K₂NaFeI₆ exhibits band gaps of 3.2 eV (spin-up) and 0.4 eV (spin-down). Both materials display ferromagnetic ordering, with total magnetic moments of 3 µB for K₂NaCrI₆ and 5 µB for K₂NaFeI₆. Optical property calculations, including the real and imaginary parts of the dielectric function, indicate strong optical absorption spanning the visible to ultraviolet energy regions. Furthermore, thermoelectric analysis predicts n-type conduction behavior for K₂NaCrI₆ and p-type behavior for K₂NaFeI₆, highlighting their potential for multifunctional energy applications.