Ab initio investigations of structural, elastic, electronic and optical properties of the fluoroperovskite TIXF₃ (X=Ca, Cd, Hg, and Mg) compounds

Ab initio calculations of Tl-based fluoroperovskite compounds TlXF₃ (X = Ca, Cd, Hg, and Mg) are carried out in the framework of Density Functional Theory (DFT). We have investigated their structural, elastic, electronic and optical properties using the full-potential linearized augmented plane wave (FP-LAPW) method. The exchange-correlation potential is examined using the generalized gradient approximation with additional Hubbard-U term for indulging on-site Coulomb interaction (GGA + U). These compounds have been found to be mechanically stable. The elastic properties such as elastic constants, bulk modulus, anisotropy factor, Poisson's ratio, and Pugh's ratio are obtained. The calculations of electronic band structure show that the TlCaF₃ and TlMgF₃ are direct while TlCdF₃ and TlHgF₃ are indirect band gap materials. The contribution of the different bands was analyzed from the total and partial density of state curves. Calculations of the optical spectra such as the real and imaginary parts of the dielectric function, optical reflectivity, absorption coefficient, optical conductivity, refractive index and extinction coefficients are performed for the energy range of 0 to 30 eV.