Ab initio study of structural, electronic, mechanical and optical properties of the tetragonal Cs2AgBiBr6 halide double perovskite

Ab-initio calculations of the structural, electronic, mechanical, optical properties and effective mass of Cs2AgBiBr6 (CABB) halide double perovskite in its tetragonal and cubic phases are presented using the full potential linearized augmented plane wave method. The generalized gradient approximation and the Trans-Blaha modified Becke-Johnson exchange potential were applied to improve the band structure and optical properties for this material. The obtained results provide predictions for the tetragonal perovskite Cs2AgBiBr6 for which no experimental and theoretical data are available except those of the refined structural parameters. Good agreement with experiment for lattice parameters demonstrates the high precision of our approach. The calculated mechanical parameters indicate the stable, ductile and anisotropic nature of both phases. More information about rigidity, bonding strength and compressibility of the CABB tetragonal phase are given. For both phases, the band structure calculations reveal semi conductor character and maximum absorption in the visible spectrum very appreciated for solar cells and optoelectronics.