A DFT Investigation of Li 3 FSe Anti‐Perovskites: Structural, Electronic, Optical, and Elastic Properties for Electrolyte in Lithium‐Ion Batteries Applications

Abstract

Density functional theory (DFT) calculations within the GGA‐PBE approximation were performed to investigate the structural, electronic, optical, and elastic properties of the anti‐perovskite Li 3 FSe for solid‐state electrolyte applications. The optimized structure is thermodynamically stable, with a formation energy of −2.66 eV per formula unit, and satisfies the Born–Huang mechanical stability criteria. The electronic structure reveals an indirect bandgap of approximately 3.8 eV, with the valence band maximum dominated by Se 4 p states. Optical calculations indicate a static dielectric constant of 4.8, a refractive index of 2.2, and strong ultraviolet absorption beginning near 4.4 eV, while maintaining low reflectivity in the visible region. The calculated elastic properties indicate a nearly isotropic response (anisotropy factor A  = 1.046) and a brittle mechanical character (Pugh ratio B / G  = 1.264, Poisson’s ratio ν  = 0.187). These results demonstrate that Li 3 FSe combines structural stability, low electronic conductivity associated with its wide indirect band, and favorable optical and mechanical properties, supporting its potential as a solid‐state electrolyte for next‐generation lithium‐ion batteries.