Ab-initio calculations of structural, vibrational, electronic and elastic properties of fluorite minerals: A computer simulation approach

Abstract

There are numerous industrial and technological uses for minerals from the fluorite group. Fluorite group minerals, according to Dana's mineralogy, are simple metallic fluorides with a cubic crystal structure that belongs to the space group Fm-3m (225). Fluorite, Stronitiofluorite, Frankdicksonite, and Fluorocronite are the members of fluorite group minerals. These are F-centered cubic minerals, also known as halides, having general formula MF2, where M = Ca, Sr, Ba, and Pb. These minerals have cubic (Fm-3m), orthorhombic (Pnma), and hexagonal (P63/mmc) phases at different pressure. In the present study, the structural optimization of CaF2, SrF2, BaF2, and PbF2 with cubic (Fm-3m) phase has been performed by Density Functional Theory (DFT) calculation using Generalized Gradient Approximation (GGA) with Quantum Espresso code. The electronic band structure of fluorite group minerals has been investigated. From the electronic band structure, it has been found that these minerals are insulator having indirect band gap. Phonon dispersion curves for CaF2, SrF2, BaF2, and PbF2 confirms that fluorite minerals in cubic phase are mechanically stable. LO–TO splitting in the phonon dispersion curves indicates that these mineral have ionic bonding. Also, lattice parameter, elastic constants, bulk modulus, Young's modulus, shear modulus, Poisson's ratio, Pugh's ratio and Cauchy pressure for fluorite minerals have been calculated using Voigt–Reuss–Hill approximation, and the results have been analyzed with experimental data.