Supercritical water at ten densities from 0.1 to 1.0 gr/cc at 1000 K using ab initio molecular dynamics simulations

Supercritical water is found inside Earth's mantle, where water is subjected to very high temperatures and pressures. It exhibits extraordinary properties, such as having a low dielectric constant and high reactivity, which stems from the breakdown of the hydrogen bond network in a supercritical state. This makes supercritical water a non-polar solvent and the basis for many innovative technologies. We investigate supercritical water at ten densities (0.1-1.0 gr/cc) at 1000 K to study the structural correlations, such as atom-resolved partial pair distributions, co-ordination numbers, bond-angle distributions and neutron scattering, and x-ray structure factors. Among the dynamical correlations, we investigate the velocity autocorrelation function, current-current correlation function, and their Fourier transforms-vibrational density-of-states and frequency dependent dielectric constant. Structural and dynamical correlations are computed from time-trajectories of the positions and velocities calculated ab initio molecular dynamics within the density functional theory framework using the SCAN exchange-correlation functional. Our results for structural correlations are compared with the neutron scattering experiments on supercritical water by Soper and collaborators [J. Chem. Phys. 106, 247-254 (1997)] and dynamical correlations in the supercritical state are compared with the inelastic neutron scattering results by Car and collaborators [J. Phys. Chem. Lett. 11, 9461-9467 (2020)].