Hydrogen Bonding in Supercritical Water Using Quantum Molecular Dynamics

In supercritical water (SCW), defined as water above its critical point (Tc = 647K, Pc = 221 bar), the nature of hydrogen bonds remains a topic of great interest. While neutron scattering studies suggest a significant reduction in hydrogen bonding in SCW, quantum molecular dynamics (QMD) simulations indicate that hydrogen bonds persist but with altered properties. We use QMD simulations with density functional theory to investigate hydrogen bonding in SCW. We introduce an electron charge density overlap based criterion to define a cutoff for H-bonds, which proves robust under extreme conditions. QMD simulations at 1,000 K across a range of densities (0.1-1.0 g/cm3) reveal that a reduced level of residual hydrogen bonding persists in SCW. Our findings provide a useful and detailed understanding of the nature of the hydrogen bond and its dynamics, including H-bond lifetimes in supercritical water, offering insights for applications in chemistry, energy, and planetary sciences.