#Density water plus#

He applied the notion of a random tetrahedral network to water. Bernal returned to the problem of liquid water. The next version of the network model was formulated by Pople, who proposed that hydrogen bond bending is the reason for the greater density of water in comparison with ice. This was a concretization of Röntgen's idea of water as a mixture of ice-like and water-like particles. They reasoned that at temperatures close to the melting point, this network is a mixture of two structures: one denser and quartz-like and the other less dense and tridymite-like (or ice-like). However, there is no explanations of what induces such a change in the proportions.īernal and Fowler put forward the idea that a three-dimensional network exists in liquid water. A change in the proportions of these complexes with temperature could explain the non-monotonic dependence of some water properties on these parameters. Some of these complexes are less dense and ice-like, whereas others are denser, proper-water complexes. Röntgen considered water to be a mixture of molecular complexes. To explain this density anomaly, several ideas have been proposed. Most liquids become monotonically denser when cooled from room temperature, but liquid water reaches its maximum density at approximately 4☌, below which it expands to become less dense as it is cooled further. It has been known for a long time that these ideas tell us nothing about what causes the negative thermal expansion at temperatures below 4☌. Our results show that most of the ideas put forward up to now do not explain the direct causes of the density anomaly of liquid water. Furthermore, we show that the behavior of excess internal energy plays an essential role in the density anomaly, and that the behavior is mainly determined by the value of the soft-repulsive potential, especially near the hard-core contact. We show that the density anomaly occurs when the value of the soft-repulsive potential at hard-core contact is in some proper range, and that the range depends on the attraction.

#Density water plus#

We consider a fluid of spherical particles with a pair potential given by a hard-core repulsion plus a soft-repulsion and an attraction. We analyze what characteristics of the pair potential cause the density anomaly on the basis of statistical mechanics and thermodynamics using a thermodynamically self-consistent Ornstein-Zernike approximation. The thermodynamic properties of substances are determined by interparticle interactions. Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, Nishihara-Cho, JapanĪlthough the density anomaly of liquid water has long been studied by many different authors, it is still not clear what thermodynamic mechanism induces the anomaly.