Comprehensive DFT + U investigation of FrFeF3 Cubic Perovskite: Structural stability, mechanical strength, and optoelectronic potential

This study presents a first-principles investigation of cubic FrFeF 3 halide perovskite using spin-polarized density functional theory with Hubbard correction (DFT+U). The structural, mechanical, thermal, electronic and optoelectronic properties of FrFeF 3 are systematically examined and compared with the corresponding characteristics of related fluoroperovskites. The compound is confirmed stable by a negative formation enthalpy (ΔH f = −3.68 eV/atom), an imaginary-frequency-free phonon spectrum, and ab initio molecular dynamics simulations at 300 K. FrFeF 3 exhibits excellent mechanical properties, including a high bulk modulus ( B₀ = 56.07 GPa) and Young's modulus (E = 95.06 GPa), alongside near-isotropic elastic behavior (A = 0.472) and borderline brittle character (B/G = 1.298, ν = 0.193). Thermal analysis reveals a high melting point (T m ≈ 1348 K) and Debye temperature (θ D = 312 K), confirming strong interatomic bonding and excellent thermal resilience. Electronic structure calculations identify FrFeF 3 as a spin-polarized magnetic semiconductor with majority and minority spin channel band gaps of 2.67 eV and 1.14 eV respectively. Moreover, the optical analysis identifies strong ultraviolet absorption, a low static refractive index (n(0) = 1.68), and minimal reflectivity (R(0) = 0.064), supporting its potential for UV optoelectronic applications. These results establish FrFeF 3 as a thermally stable, mechanically robust, and optically active spin-polarized magnetic semiconductor with promise for high-performance functional devices.