DFT study of structural, elastic and optoelectronic characteristics of novel Rb₂CaSnX₆ (X = Cl, I) double halide perovskites for optoelectronic applications

We evaluate the structural, optoelectronic, and mechanical characteristics of the novel Rb₂CaSnCl₆ and Rb₂CaSnI₆ through density functional theory within the WIEN2K framework. The formation energies and volume optimization provide evidence for the structural stability of these compounds. The optimized lattice constants for Rb₂CaSnCl₆ and Rb₂CaSnI₆ are found to be 11.21 Å and 12.45 Å, respectively while their respective formation energies are calculated as − 2.5 Ry and − 1.6 Ry. Similarly, the grounds state energies are calculated − 31,184.32 Ry and − 111,074.60 Ry. We find that Rb₂CaSnCl₆ is an insulator with a bandgap energy of 3.50 eV when the modified Becke-Johnson (mBJ) approximation is applied and that Rb₂CaSnI₆ is directly semiconducting with a wide bandgap energy of 2.70 eV. Evaluations of mechanical stability show that both materials are mechanically stable and their constituent atoms are bound together by ionic interactions, indicated by the positive value of Cauchy’s pressure: 46. 32 and 21.93 for Rb₂CaSnCl₆ and Rb₂CaSnI₆, respectivley. Nevertheless, our investigation showed that Rb₂CaSnI₆ behaves as a ductile material while Rb₂CaSnCl₆ is brittle. We also investigate a variety of optical characteristics such as dielectric function, refraction, reflectivity, energy loss function, and extinction coefficient. The static dielectric function was found to be 2.9 and 4.3 for Rb₂CaSnCl₆ and Rb₂CaSnI₆, respectively. Rb₂CaSnI₆ exhibited greater optical conductivity, indicative of it being a better metallic than the Rb₂CaSnCl₆. The optical investigation suggests that these materials have a great deal of promise for cutting-edge optoelectronic applications, especially in the ultraviolet (UV) spectrum due to their large electronic band gap. These results offer a solid basis for future research into these intriguing materials by experimentalists.