First-principles analysis of vibrational modes of calcite, magnesite and dolomite

Calcite, magnesite and dolomite are important in Earth's evolutionary history, so they are significant in sediments and biominerals. As we know, the experimental investigations of calcite, dolomite, magnesite with Raman spectra are widespread. In order to show microprocess about Raman spectra, the first-principles vibration calculations deserve further discussion. So, the first-principles density functional perturbation theory is employed to calculate the phonon dispersion, IR spectrum, Raman spectrum, thermodynamic properties and dielectric permittivity. The vibration modes of phonon dispersion curves are investigated through symmetry system. The vibration type from group theory is used to discuss the IR activity and Raman activity, where the minerals space group are R3¯c, R3¯c and R3¯ for clacite, magnesite and dolomite, respectively. The calculated phonon dispersions show that minerals with ionic and covalent bonds are dynamically stable. The vibration analysis of IR modes and Raman modes reveals the strongest covalent bond in (001) plane, and it can produce bigger shear modulus. In addition, the differently cationic masses have a little effect on thermodynamic and dielectric properties for minerals. The investigated results in this paper can promote the analysis of minerals at microscopic level, where the information of vibration can expound the stably combinative direction of electron cloud of minerals. So it can present the macroscopically mechanical property, which would help researchers to research earth mantle.