Theoretical investigation of structural, electronic, elastic, thermodynamic, and optical characteristics of novel Fluoro-perovskites FrHF3 (H = Mg, Ca) using DFT calculations

This study investigates the structural, mechanical, electronic, optical, and thermodynamic properties of FrHF 3 (H = Mg, Ca) perovskites using Density Functional Theory (DFT) with the Generalized Gradient Approximation (GGA) and the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional. The structural and mechanical stability of these phases is confirmed by their negative formation enthalpy, tolerance factor, and positive phonon dispersion curves, indicating their potential for experimental synthesis. The compounds exhibit direct band gaps, with an increase from 5.932 eV (FrMgF 3 ) to 6.47 eV (FrCaF 3 ), influencing their optoelectronic behavior. The electronic structure was analyzed using partial (PDOS) and total (TDOS) density of states to assess electron localization across different energy bands. Additionally, the ELATE program was employed to evaluate elastic tensors and generate 2D and 3D representations. High bulk and Young's moduli suggest promising industrial applications for FrHF 3 (H = Mg, Ca). The analysis of mechanical properties, including Pugh's ratio, Poisson's ratio, and Cauchy pressure, reveals that FrMgF 3 is ductile (Poisson's ratio = 0.31), whereas FrCaF 3 is brittle (Poisson's ratio = 0.25). Both compounds exhibit anisotropic characteristics. Optical properties, including dielectric function, absorption coefficient, optical conductivity, loss function, refractive index, reflectivity, extinction coefficient, transmittance, and absorbance, were examined. The materials demonstrate strong UV absorption, 327,109.25 cm −1 for FrMgF 3 and 302,462.55 cm −1 for FrCaF 3 , as well as high optical conductivity, with peak values of 6.66 (1/fs) and 6.30 (1/fs) for FrMgF 3 and FrCaF 3 , respectively. Additionally, their significant absorption index makes them suitable for applications in sensors, photodetectors, optoelectronics, and other optical technologies. Debye temperatures exceeding 200 K indicate high sound velocities, elevated melting points, and low minimum thermal conductivities, suggesting potential use in thermal barrier coatings (TBCs). Thermodynamic properties, such as specific heat capacity and entropy, were evaluated across a temperature range of 0–1000 K.