A Density Functional Theory Insight into Structural, Mechanical, and Optical Properties of Rb₂LiTlF₆ Double Perovskite

Abstract

The density functional theory (DFT) is applied to systematically investigate the geometrical structure, electronic, mechanical, vibrational, and optical properties of double perovskite Rb 2 LiTlF 6 in its cubic phase. To the best of one's knowledge, many physical properties of this compound are still not well established or not yet investigated; such as phonon properties, mechanical behavior, thermal properties, and so on. In this work, the stability of Rb 2 LiTlF 6 is explored by looking at its thermodynamical behavior through calculation of formation energy, cohesive energy, Goldschmidt tolerance factor, and phonon dispersion. Its mechanical properties are examined based on various characterization descriptors such as the independent elastic coefficients, bulk, shear, and Young's modulus, ratios such as Pugh and Poisson's, Kleinnman parameter, Zener anisotropy factor, Debye temperature, and melting temperature. Sound velocity in this material is predicted from the values of the bulk and shear modulus obtained. Thermal expansion coefficient at finite temperatures are obtained using the approach of quasi‐harmonic approximation. Its electronic property is also investigated using generalized gradient approximation and also hybrid functionals. At a later stage, its optical behavior upon the effect of light excitation is explored using the many body pertubation theory approximation. Having envisioned this material as a wide band gap semiconductor, it can be useful in numerous applications such as designing the top‐cell of tandem photovoltaic configuration, photodetection, and light emitting diodes. It is strongly believed that this work will provide a helpful guidance for future experimental and theoretical investigations of this material.