<scp>DFT</scp> Insights Into the Structural, Stability, Elastic, and Optoelectronic Characteristics of <scp> Na ₂ LiZF ₆ </scp> (Z = Ir and Rh) Double Perovskites for Sustainable Energy

Halide perovskites have gained significant attention due to their tunable bandgaps and environmentally friendly properties, making them strong candidates for advanced optoelectronic applications. In this study, we employed the FP-LAPW method to explore the structural, electronic, and optical properties of Na₂LiZF₆ (Z = Ir and Rh). Our findings confirm the stability of the cubic phase through a Goldschmidt tolerance factor of 0.99 and negative formation energies of -3.34 Ry for Na₂LiIrF₆ and -3.22 Ry for Na₂LiRhF₆. Additionally, phonon dispersion analysis verifies their dynamic stability. Mechanical analysis indicates that these materials are structurally robust, with bulk moduli of 84.21 and 80.48 GPa, while their ductile nature is supported by Pugh's ratios of 2.21 and 2.41, respectively. From an electronic perspective, both compounds exhibit indirect bandgaps of 4.05 and 3.98 eV, making them suitable for UV applications. Optical studies further reveal strong UV absorption, with static dielectric constants of 1.42 and 1.50, along with refractive indices (n(0)) of 1.19 and 1.22. These characteristics make Na₂LiZF₆ (Z = Ir and Rh) promising candidates for next-generation UV photodetectors and light-emitting devices.