Thermodynamic properties of CaCO3–SrCO3–BaCO3 liquids: a molecular dynamics study using new empirical atomic potentials for alkaline earth carbonates

Abstract

Thermodynamic modeling offers a powerful framework for studying melting reactions of carbonated mantle systems across a wide range of compositions, pressures, and temperatures. Such modeling requires knowledge of the standard state thermodynamic properties of the pure alkaline earth carbonate liquid components, which are difficult to determine experimentally due to their instability at 1 bar. Atomistic simulations offer a solution to these experimental difficulties by providing access to metastable states and supplying constraints on thermodynamic properties. We developed an empirically-derived potential model for the simulation of alkaline earth carbonates (MgCO3, CaCO3, SrCO3 and BaCO3), emphasizing the accurate simulation of the standard state thermodynamic properties of carbonate liquids. Molecular dynamics (MD) simulations of liquids in the CaCO3–SrCO3–BaCO3 system are performed over a geologically relevant temperature–pressure range (1100–3400 K and 0–43 GPa). Simulation data for each of these three components (up to a maximum of 2300 K and 30 GPa) are fitted to a temperature-dependent third-order Birch–Murnaghan equation-of-state to estimate their standard state thermodynamic properties. With a few exceptions, calculated properties agree well with available estimates from experiments and/or first-principles MD simulations. Exploration of binary mixtures supports ideal mixing of volumes, heat capacities, and compressibilities, reflecting the common liquid structure and pressure–temperature evolution for these three components. The success of this new model for CaCO3–SrCO3–BaCO3 liquids suggests that it can accurately predict the properties of MgCO3-bearing liquids, where experimental data are unavailable.