First-principle studies of electronic, elastic and vibrational properties of barytocalcite and paralstonite

Abstract

The crystal structure, electronic, elastic and vibrational properties of two natural BaCa(CO3)2 polymorphs (barytocalcite and paralstonitis) were studied by the density functional theory methods using the hybrid B3LYP and gradient PBE functionals, taking into account the dispersion correction D3 to the total energy in the basis of localized orbitals of the CRYSTAL package, under the pressure about 3 GPa. It is shown that the cell volume of hexagonal paralstonite obtained by the PBE-D3 method per formula unit is 0.065 Å3 larger, and the total energy is 0.011 eV lower than that of a monoclinic barytocalcite. The parameters of the equation of state in the Birch-Murnaghan form are determined. The elastic constants of single crystals and, in the Voigt-Royce-Hill approximation, the elastic moduli and elastic wave velocities of polycrystals are calculated. In the electron energy spectrum, the width of the upper valence band is 0.85 eV in barytocalcite, and 0.94 eV in paralstonite, while the band gap is 4.85 eV and 4.36 eV, respectively, and it decreases with increasing pressure at rates of − 0.01 and − 0.02 eV/GPa. The frequencies and intensities of normal long-wave oscillations are calculated with the B3LYP functional. It is shown that qualitative differences in the spectra of infrared absorption and Raman scattering of light for two phases should be sought in the range of 1300÷1580 cm−1 in the region of intramolecular vibrations, and for the spectra of infrared absorption in the region of 260÷310 cm−1, and for light scattering in the range of 130÷180 cm−1 in the region of lattice vibrations.