First-principle insight into the structural, electronic, elastic and optical properties of Cs-based double perovskites Cs 2 XCrCl 6 (X = K, Na).

This study communicates the theoretical investigations on the cubic double perovskite compounds Cs 2 XCrCl 6 (X = K or Na). Density functional theory (DFT) calculations were carried out using the TB-mBJ approximation. These compounds were found to be stable in the cubic perovskite structure having lattice constants in the range of 10.58-10.20. The stability of the investigated materials was assessed by the Gold-Schmidt tolerance method, which resulted in the tolerance factor values of 0.891 and 0.951 for Cs 2 KCrCl 6 and Cs 2 NaCrCl 6 , respectively. The calculated values of the elastic constants C 11 , C 12 , and C 44 of the cubic compounds studied by our research team confirm the elastic stability. The values of the formation energies were also calculated for both the compounds and were found in the range from -2.1 to -2.3. The electronic behavior of the presently investigated materials was examined by inspecting their band structures and the density of states. It was observed that both the materials have half-metallic nature. To check the suitability of the studied compounds in optical applications, we determined the real and imaginary parts of their respective dielectric functions, absorption coefficients, optical conductivities, refractive index, and reflectivity as a function of a wide range of incident photon energies up to 40 eV.