Comparative analysis of band gap using different approximations, structural, mechanical and optical behaviour analysis of lead free double halide perovskites Cs2AgBiBr6 using DFT approach

Lead-free double perovskite have drawn considerable attention of researchers for optoelectronic and photovoltaic applications due to their better stability and non-toxicity. In this study, ${Cs}_2{AgBiBr}_6$ double perovskite has been investigated using density functional theory (DFT) approach. Although the physical parameters of this material have been analyzed by many researchers previously but their results particularly band gap showing diverse nature. Therefore, primary purpose of this work is to calculate and compare physical parameters through different approximations along with relevant exchange correlational functional. Structural and electronic parameters are determined by employing different approximations after finding the stable geometry. The calculated lattice parameters, formation energy, energy band gap and density of states are compared with literature and calculated parameters using different approximations. The calculated band gap for ${Cs}_2{AgBiBr}_6$ through GGA-PBE (without SOC), HSE03 and TB-mBJ are 1.998 eV, 1.992 eV and 2.227 eV respectively, which are very close to the experimental results. For further understanding about the mechanical and optical behaviour of the considered compound, optical and mechanical parameters such as dielectric function, absorption, conductivity, reflection, refractive index, shear modulus, Poisson's ratio, bulk and young's modulus respectively etc is studied. This study will provide an insight for the investigation find suitable physical parameters including structural, electronic, optical and mechanical properties using an appropriate approximation method for optoelectronic application.