Unveiling the Role of Halide Variation in Ba 3 BiX 3 (X = I, Br, Cl, and F) Perovskites Through First Principle DFT Approach: Tuning the Physical Properties

ABSTRACT Structural, mechanical, and optical properties of the Ba 3 BiX 3 (X = I, Br, Cl, and F) compounds were studied in terms of first‐principles density functional theory (DFT) calculations within generalized gradient approximation‐Perdew‐Burke‐Ernzerhof (GGA‐PBE) assumptions using Quantum ESPRESSO. Structural investigation establishes the cubic nature of the Ba 3 BiX 3 (X = I, Br, Cl, and F) compounds that have stable geometries, and the lattice parameters reduce sequentially with halogen replacement. Investigation of the electronic properties using the electronic property analysis shows that Ba 3 BiX 3 (X = I, Br, Cl, and F) compounds belong to the category of direct bandgap, and the bandgap decreases systematically with heavier halogens, whereas the effect of spin‐orbit coupling is dominant on the electronic structure. Ba 3 BiF 3 has the highest bandgap and smallest effective masses of all of them, meaning the best optoelectronic prospects. The dynamical stability of the compounds is confirmed by phonon dispersion analysis and vibrational frequencies. The compounds have stiffer, harder, and more thermally stable structures as determined by both mechanical and thermodynamic analyses. Optical investigations of Ba 3 BiX 3 (X = I, Br, Cl, and F) compounds provide tunable dielectric, highly absorbing response, and refractive index variation, with the best visible response in Ba 3 BiI 3 and the best UV performance in Ba 3 BiF 3 .