FIRST-PRINCIPLES INVESTIGATION OF THE STRUCTURAL, ELECTRONIC, MECHANICAL, AND OPTICAL PROPERTIES OF HYPOTHETICAL Cs2BeInX6 (X = Cl AND I) DOUBLE PEROVSKITES

Abstract

Lead-free halide double perovskites have attracted considerable interest because of their potentially useful electronic and optical properties. In this study, the structural, electronic, mechanical, and optical properties of the hypothetical Cs₂BeInX₆ (X = Cl and I) double perovskites were investigated using first-principles density functional theory calculations within the CASTEP framework. Both compounds were optimized in the cubic Fm-3m structure, with lattice parameters of 9.75 Å for Cs₂BeInCl₆ and 10.80 Å for Cs₂BeInI₆. Their calculated tolerance factors of 0.92 and 0.89, respectively, support the structural feasibility of the proposed perovskite phases. The calculated elastic constants satisfy the Born mechanical-stability criteria. Cs₂BeInCl₆ exhibits greater rigidity than Cs₂BeInI₆, with bulk, shear, and Young’s moduli of 270.08, 230.21, and 369.81GPa, respectively. Electronic band-structure calculations indicate indirect semiconducting behavior, with band gaps of 0.97 eV for Cs₂BeInCl₆ and 0.85 eV for Cs₂BeInI₆. The density-of-states results further support the semiconducting character of both compounds. Optical calculations reveal pronounced absorption in the ultraviolet region, with maximum absorption coefficients of approximately 3.5×10⁵ and 3.0×10⁵ cm for Cs₂BeInCl₆ and Cs₂BeInI₆, respectively. These findings indicate that the proposed compounds possess potentially useful mechanical, electronic, and ultraviolet optical characteristics, making them suitable candidates for further theoretical and experimental investigation.