High-pressure structural phase transitions and mechanical properties of calcite rock

In the present work, a state of the art first principles theory is used to examine the structural and mechanical properties of calcium carbonates CaCO3. Our calculations allowed full structural relaxation, which permits an appropriate evaluation of material properties at ambient conditions as well as under hydrostatic pressure. Compared to experimental measurements the calculated ground state properties show a suitable agreement. By performing a structural phase stability analysis, we were able to predict both first and second order phase transitions that calcium carbonates minerals undertake under hydrostatic pressure. The first one occurs between the calcite and aragonite phases at 3.3 GPa and the second one between the aragonite and post-aragonite phases at ∼40 GPa. The previous value agree very well with experimental one (40 GPa) reported by Ono et al. In order to verify the reliability of such phase transitions, we study the mineral high pressure stability by means of mechanical properties behaviour. Both transversal wave velocity and elastic moduli show an unexpected decrease at phase transition pressure range.