A computational study of the physical properties of AgXF3 (X= Ca and Sr) fluoro-perovskites for energy conversion: GGA and meta-GGA insight

This work employs density functional theory with both GGA and meta-GGA functionals to investigate the structural stability, optoelectronic and thermoelectric properties of AgXF 3 (X=Ca and Sr) perovskites. The optimized lattice parameters decrease and the energy formation increases with the meta-GGA functionals compared to GGA functional. The band structure calculations indicate a semiconducting nature with an indirect band gap ( M - Γ symmetry points) for GGA, SCAN, rSCAN and r 2 SCAN. The band gap increases when using the meta-GGA functionals compared to GGA, and further increases with the use of HSE. Employing the GGA functional, the computed elastic properties show the mechanically stable and ductile nature of these compounds, which are characterized by metallic bonds. Optical properties, including the imaginary and real parts of the dielectric function, refractive index, reflectivity, and absorption coefficient, were computed and analyzed within the range of 0 to 20 eV using both GGA and meta-GGA functionals. Results indicate a diminished optical response with meta-GGA compared to GGA. The observed low reflectivity and high light absorption suggest that these compounds are more suitable in solar energy and optoelectronic applications. The thermoelectric properties of AgCaF 3 and AgSrF 3 , including the Seebeck coefficient, electrical and thermal conductivity and figure of merit were studied under the constant relaxation time. The maximum value of ZT of 0.926 (0.94) was obtained at 550 K (425 K) for AgCaF 3 (AgCaF 3 ) with the GGA functional. The obtained results show that the meta-GGA functionals provide better accuracy at lower temperatures, while GGA functional perform better at higher temperatures. • The optimized lattice parameters decrease and the energy formation increases with the meta-GGA functionals compared to GGA functional. • The band gap increases when using GGA to meta-GGA functionals compared to GGA, and further increases with the use of HSE. • Results indicate a diminished optical response with meta-GGA compared to GGA. • The obtained results show that the meta-GGA functionals provide better accuracy at low temperatures, while GGA functional perform better at high temperatures.