Dielectric properties of water in the Earth’s interior vary widely

Little is known about the solvation properties of water under immense pressure and elevated temperatures, deep in Earth’s interior. One challenge persisting in these studies is the difficulty in obtaining the static dialectic constant of water under these extreme conditions. To fill in this information gap, Hou et al. used a neural network dipole model combined with molecular dynamics to study the dielectric properties of water under high pressure and high temperature.

The data-driven machine learning technique enabled the researchers to calculate the dielectric constant of supercritical water from 1 to 15 GPa and 800 to 1400 K. A database was then developed based on the information gathered across these pressure and temperature ranges.

“This approach can be readily applied to study other molecular fluids,” said author Ding Pan. “It would be interesting to see if it works for fluid mixtures, and how dielectric properties change with mixtures.”

The authors found that the dielectric constant of supercritical water can vary by one order of magnitude within the upper mantle. This indicates that the crucial solvation properties of water vary across different depths.

“The accuracy of our neural network dipole model solely depends on the accuracy of training data,” said Pan. “In the future, we may use some high-level theories, such as hybrid functionals, to generate the training data and we may implement the predicted dielectric constant of water into the Deep Earth Water model, which is widely used by the geochemistry community to study water-rock interactions in Earth’s interior.”

Source: “Dielectric constant of supercritical water in a large pressure-temperature range,” by Rui Hou, Yuhui Quan, and Ding Pan, Journal of Chemical Physics (2020). The article can be accessed at https://doi.org/10.1063/5.0020811 .