Effect of the local hydrogen bonding network on the reorientationaland translational dynamics in supercritical water

摘要

Molecular dynamics simulations have been performed in a wide range of densities along a nearcritical isotherm of supercritical water in order to reveal the interconnection between the localhydrogen bonding (HB) network and several related dynamic properties. The results obtained haverevealed a significant slowing down of reorientational dynamics of the water molecules as the valueof the number of hydrogen bond per molecule increases and this is reflected on the increase in thereorientational correlation times. The calculated reorientational times exhibit also an increasingtrend by increasing the bulk density, and this effect is more pronounced in the case of the first-orderLegendre reorientational correlation functions. A clear nonlinear dependence of the librational modefrequencies of the water molecules on the augmented local density around them has also beenrevealed. This result could be regarded as an additional support of experimental observationssuggesting the use of a nonlinear relation when analyzing the density dependence of spectroscopicpeak frequencies in order to extract information about local density augmentation in supercriticalfluids. The HB dynamics have been also investigated, revealing a plateau in the calculated HBlifetimes at intermediate and higher liquidlike densities and a small increase at low, gaslikedensities.