Ab initio exploration of the structural, elastic, electronic and optical properties of a new layered perovskite-type oxyfluoride: CsSrNb2O6F

We report and discuss the results of a detailed ab initio investigation of the structural, elastic, electronic and optical properties of a new layered perovskite-type oxyfluoride: CsSrNb2O6F. The calculated ground state lattice parameters are in excellent agreement with the available experimental counterparts. The six predicted distinct single-crystal elastic constants satisfy the mechanical stability criteria. From the calculated single-crystal elastic constants, a set of related properties, viz., the bulk modulus, shear modulus, Young's modulus, anisotropic and isotropic sound velocities, elastic anisotropy, malleability and Debye temperature, are determined. The title compound is found to be ductile with strong elastic anisotropy. Considering that the measured values are always determined with uncertainties of various origins, one can state that the calculated fundamental indirect bandgap value of similar to 2.9 eV and the onset of direct optical transitions at similar to 3.6 eV are in acceptable agreement with a prior measurement giving a bandgap of similar to 3.4 eV. Particular attention has been given to the bonding properties and distribution of the electron density in the space between the crystal lattice ions through the calculation of density of states diagrams, bond lengths and the charge density distribution. The linear optical parameters of the considered compound, including the complex dielectric function, absorption coefficient, refractive index and optical reflectivity, are predicted for incident electromagnetic radiation polarized parallel to the [100] and [001] crystallographic directions. It is noted that CsSrNb2O6F exhibits a strong optical anisotropy.