Pressure induced phase transitions and elastic properties of CaCO3 polymorphs: a density functional theory study

First-principles calculations, based on density functional theory, were carried out to investigate phase transitions, structural and elastic properties of three polymorphs of calcium carbonate, in the pressure range up to 40 GPa. Our calculations led to the following stability sequence: calcite-IIIb -> calcite-III -> calcite-IIIb -> calcite-VI, where phase transitions of the first order occur at 4.3 GPa, 14.9 GPa and 18.2 GPa, respectively. From 4.3 to 40 GPa, the elastic properties, the acoustic wave velocities and the Debye temperature of each polymorph exhibit a linear dependence over pressure. A nonlinear behavior is observed from 2.0 to 4.3 GPa for the properties of calcite-IIIb. As there are no available experimental data on the elastic properties of calcite-III, calcite-IIIb, calcite-VI and their pressure dependence, our present findings can serve to a better understanding of the behavior of calcium carbonate in the Earth's mantle.