A Comprehensive Thermoelectric Performance of Li‐Based Double Perovskites Na 2 LiMF 6 (M = Rh, Ir) for Sustainable Energy Applications via Density Functional Theory Approach

The tunable bandgaps and environmentally benign properties of halide perovskite structures have attracted tremendous attention, making them appealing for a variety of cutting‐edge applications, especially in optoelectronics and thermoelectric. The structural diversity and potential functional features of double perovskites, like Na 2 LiMF 6 (M = Rh, Ir), make them interesting. The structural integrity of the cubic phase for both compounds is supported by a computed tolerance factor of 0.92. Additionally, ideal volume curves and negative formation energies support their thermodynamic stability. Mechanical evaluations indicate that these materials are ductile, anisotropic, and mechanically stable. Strong ultraviolet absorption is found in optical studies, indicating its applicability to UV‐based optoelectronic systems. Additionally, their high room temperature power factors indicate their potential for use in thermoelectric applications. Density functional theory approach was carried out employing the full‐potential linearized augmented plane wave methodology. The semi‐classical Boltzmann transport theory was applied to evaluate the thermoelectric properties. The electronic structure and bandgap were precisely described using the Tran‐Blaha modified Becke‐Johnson potential. To determine the impact of spin–orbit coupling on the material's characteristics, bandgap was also evaluated with its incorporation. Furthermore, the elastic constants were computed to derive key elastic properties, allowing for an assessment of mechanical stability and the degree of anisotropy. Finally, a study of the optical response was conducted by calculating various parameters including the absorption coefficient, refractive index, energy loss function, and polarization across a photon energy spectrum of 0–10 eV.