Local structural fluctuations, hydrogen bonding and structural transitions in supercritical water

The contribution of hydrogen bonding interactions to the formation of local density inhomogeneities in supercritical water at near-critical conditions has been extensively studied by means of molecular dynamics simulations. The results obtained have revealed the strong effect of water molecules forming one and two hydrogen bonds on the determination of the local density augmentation in the fluid. The local structural order has also been studied in terms of the trigonal. and tetrahedral order parameters, revealing the correlation between local orientational order and hydrogen bonding. The dynamics of the structural order parameters exhibit similarities with local density ones. The local structural analysis performed in terms of nearest neighbors around the individual molecules provides additional significant evidence about the existence of a liquid-like to gas-like structural transition in supercritical water at the density range close to 0.2 rho(c), further supporting previous suggestions based on the interpretation of experimental thermodynamic data.