Calcium carbonate at high pressures and high temperatures: a first-principles investigation

We present a theoretical investigation, within the density functional theory and the quasi-harmonic approximation framework, on the stability properties of calcium carbonate (CaCO3) at the thermodynamic conditions of the Earth’s lower mantle. We initially explored the structural properties of a low-pressure phase (aragonite) using three different approximations for the exchange-correlation potential, and find that all properties are better described, when compared to recent experimental data, by using the one that takes into account the van der Waals interactions. We used this approximation to compute the free energy of this mineral in several crystalline phases, and explored the respective thermodynamic properties at high temperatures and high pressures. The results on phase stability, thermal expansivity, specific heat, bulk modulus, and mass density were compared to available experimental data. Then, we built the phase diagram for this mineral and discussed its impact on the Earth’s mantle properties.

Source: Physics of the Earth and Planetary Interiors - November 21, 2019 Category: Physics Source Type: research