Structural, elastic, electronic, and optical properties of lead-free halide double perovskites Cs₂BꞌBꞌꞌBr₆ (BꞌBꞌꞌ: BeMg, CdBe, CdGe, GeMg, GeZn, MgZn): Ab initio calculations

In our study, we theoretically investigated the structural, elastic, electronic, and optical characteristics of halide double perovskites (DPs) Cs₂B'B''Br₆ (B'B'': BeMg, CdBe, CdGe, GeMg, GeZn, MgZn). Structural stabilities were assessed based on the enthalpy of formation, tolerance factor, and elastic constants. Ductile and brittle behavior was examined using Poisson and Pugh's ratios. Based on electronic calculations, it has been concluded that Cs₂B'B''Br₆ double perovskites with B'B'' as BeMg or CdBe exhibit direct bandgaps, whereas those with B'B'' as CdGe, GeMg, GeZn, or MgZn display indirect bandgaps. Additionally, we thoroughly investigated the optical properties of double perovskites by analyzing all their parameters in the energy range spanning 0 to 13 eV. Primary absorption was noted in the ultraviolet (UV) region.

In this work, all calculations were performed using the Wien2k package. The generalized gradient approximation (GGA) and the modified Becke-Johnson (mBJ) method were employed to describe the exchange–correlation interactions.