Calculation of infrared and Raman vibration modes of magnesite at high pressure by density-functional perturbation theory and comparison with experiments

摘要

We predict the IR-TO, IR-LO and Raman modes (wave numbers and intensities) of magnesite (MgCO₃) up to 50 GPa, at T = 0 K, using the density-functional perturbation theory up to a third order perturbation, under the harmonic assumption. The predicted IR-TO and Raman mode wave numbers, the mode Grüneisen parameters and the Davydov splittings are systematically compared with experimental data for all modes up to the pressures of 10–30 GPa and for some modes up to 50 GPa. Existing experiments allow extending this comparison only to IR-LO wave numbers of the E _u (ν₃) asymmetric-stretch mode, confirming the odd experimental behavior of this mode at very high pressures. Predicted IR-TO, IR-LO and Raman intensities up to 50 GPa are just tabulated, but data are missing for their comparison with precise experiments. However, the generally good agreement observed between numerical results and experimental data, when their comparison is possible, suggests that first-principles methods are a major help to predict the entire spectrum up to very high pressures.