DFT-based study of structural, mechanical, electronic, thermodynamic, and optical properties of wide band gap RbSrX3(X=F, Cl, Br, I) Halides: Promising materials for optoelectronic applications

In this study, we investigated the structural, optical, electrical, thermodynamic, and mechanical properties of RbSrX₃ (X = F, Cl, Br, I) using density functional theory (DFT). The formation energy, Goldschmidt tolerance factor ${\tau }_G$ , octahedral factor ($\mu )$ and Gibbs free energy unveils a high level of thermodynamic and structural stability. The phonon dispersion curves show only positive frequencies, indicating stable lattice vibrations. The quasi-harmonic Debye model reveals temperature effects on entropy, enthalpy, and heat capacity. An indirect band gap of 5.71eV (RbSrF₃),4.62eV (RbSrCl₃),3.87eV (RbSrBr₃) and 3.32eV (RbSrI₃) is found using GGA-PBE, while the corresponding HSE calculated band gaps are 7.97eV (RbSrF₃),5.72eV (RbSrCl₃),5.43eV (RbSrBr₃) and 4.55eV (RbSrI₃) respectively. The mechanical stability was confirmed using the Born stability criterion, which also demonstrated the material's strength, ductility, brittleness, and anisotropic behavior. The study explores absorption, polarization, refractive index, and energy loss from 0 to 14 eV. The dielectric constant has been examined to identify the highest absorption of incident light in the UV spectrum. The band gap values of these compounds indicate that they absorb radiation in the ultraviolet region; thereby, substituting from fluoride to iodide causes a gradual decrease in the band gap. Mulliken and charge density analysis show charge transfer and strong Sr–X hybridization. This suggests that these materials could be suitable for UV optoelectronic applications.