H2O CO2

The importance of water for life can be rivalled only by its importance in geological processes.
Aqueous fluids are the most efficient agents of mass transport in the Earth’s crust and upper mantle. In the geochemical cycles of C, S, Cl, and even metals such as Li, aqueous fluids play important roles. Supercritical aqueous fluids are part of a series of processes connecting the geochemical cycles of the Earth’s crust and mantle. The presence of such fluids reduces the melting point of the mantle thus leading to partial melting. These melts may rise and contribute to the formation of new crust. Even if melting is not present, aqueous fluids interact with the mantle. Fluid-rock interactions in the deep mantle have been linked to the formation of diamonds. Due to the lack of thermodynamic data at high pressures and temperatures, our understanding of the rock-fluid interactions in the deep mantle is limited.

Fluids lack long-range order (figure 1) thus making it difficult to study them experimentally at high pressures. Computational approaches are free of such restrictions. The attractive forces and chemical bonds at play in water at extreme conditions are poorly understood and are difficult to model. Van der Waals interactions play key roles in the dynamical and structural properties of water, but traditional functionals used in ab initio molecular dynamics ignore these interactions. In order to ensure the accuracy of our simulations we employ a non-local functional that includes van der Waals making our simulations one step closer to nature. Using this functional we employ Born-Oppenheimer molecular dynamics to study the equation of state of the C-H-O system in its fluid states. The results of our molecular dynamics simulations will also be used to determine structural properties of the fluids, the speciation of C, and many more other properties of interest.

Our work will provide data that will help develop our understanding of rock-fluid interactions in the deep mantle, the carbon cycle, and shed a brighter light on the formation of diamonds.

Abstract (Structure and dynamics of water-CO2 mixtures at elevated temperatures and pressures)