A random network model for water

Abstract

A random network model for liquid water is discussed. This model, which uses information derived from studies of crystalline ices, amorphous solid water, and liquid water, is based on two assumptions, one of which refers to structure and the other to the dynamics of the molecular motion. These assumptions are (i) there is a continuous, albeit distorted, network of hydrogen bonds in the liquid, and (ii) it is meaningful to describe the molecular motion by using two distinct time scales. It is shown how adoption of these assumptions leads to the definition of a random network potential, and to rather good descriptions of the 00 distribution function, the dielectric constant, and the bulk thermodynamic properties of liquid water. Despite its successes, the random network model fails to describe adequately some of the properties of liquid water; these discrepancies are discussed from the point of view of modifications needed to improve the model.

Hydrogen bonds in liquid water are broken only fleetingly

“…Support for this estimate comes broadly, from latent heats of melting and vaporization, from x-ray and neutron scattering, and in very detailed form from molecular dynamics (MD) simulations (1)(2)(3). The role of nonhydrogen-bonded configurations (NHBs) in water's rapidly changing structure remains uncertain, lying at the heart of differences between mixture and continuum models of water (1,(3)(4)(5)(6)(7)(8). Implicitly or explicitly, the interpretation of many experiments and MD simulations conceives of NHBs as broken or dangling hydrogen bonds, stable species that interconvert with a hydrogen-bonded configuration (HB) at a rate determined by the free energy barrier separating them.…”

Multi‐Nuclear Relaxation Time Studies in Undercooled Aqueous Electrolytes

“…Hindered translations and rotations can be considered as thermal excitations of the quasistatic H-bond network [8,9]. At high temperatures these quasi-lattice vibrations (QLV) are strongly damped.…”

“…Heitjans et al studied the system LiCl/7 D 2 0 with p-radiation detected NMR. The spin-lattice relaxation rate of 8 Li was measured to temperatures far below the glass transition temperature of the system. They could find indications for two dynamic processes and suggest that the local anisotropic modes are responsible for the weak relaxation rate maximum observed below the glass transition.…”

Which Shape Characteristics of the Intermolecular Interaction of Liquid Water Determine Its Compressibility?

“…It is well-known that almost none of the ideas put forward [41][42][43][44][45][46][47][48][49][50][51][52][53][54] explain what causes the negative thermal expansion at temperatures below 4 • C. For example, one claim is that the tetrahedral structure of ice causes the density anomaly, but there is no evidence for this. As a counter analogy, consider a folding umbrella.…”