Correlation of Structural Order, Anomalous Density, and Hydrogen Bonding Network of Liquid Water

Abstract

We use extensive molecular dynamics simulations employing different state-of-the-art force fields to find a common framework for comparing structural orders and density anomalies as obtained from different water models. It is found that the average number of hydrogen bonds correlates well with various order parameters as well as the temperature of maximum densities across the different models, unifying apparently disparate results from different models and emphasizing the importance of hydrogen bonding in determining anomalous properties and the structure of water. A deeper insight into the hydrogen bond network of water reveals that the solvation shell of a water molecule can be defined by considering only those neighbors that are hydrogen-bonded to it. On the basis of this view, the origin of the appearance of a non-tetrahedral peak at a higher temperature in the distribution of tetrahedral order parameters has been explained. It is found that a neighbor that is hydrogen-bonded to the central molecule is tetrahedrally coordinated even at higher temperatures. The non-tetrahedral peak at a higher temperature arises due to the strained orientation of the neighbors that are non-hydrogen-bonded to the central molecule. With the new definition of the solvation shell, liquid water can be viewed as an instantaneously changing random hydrogen-bonded network consisting of differently coordinated hydrogen-bonded molecules with their distinct solvation shells. The variation of the composition of these hydrogen-bonded molecules against temperature accounts for the density anomaly without introducing the concept of large-scale structural polyamorphism in water.

Effect of Uranyl Ion Concentration on Structure and Dynamics of Aqueous Uranyl Solution: A Molecular Dynamics Simulation Study

“…Therefore, the decrease in overall diffusivity of water in the presence of uranyl ion is a consequence of long-range effect. The effect of finite concentration of the actinyl ions on the tetrahedral structure 25 of water is an interesting aspect to investigate, and work in this direction is in progress. …”

Effects of Concentration on Like-Charge Pairing of Guanidinium Ions and on the Structure of Water: An All-Atom Molecular Dynamics Simulation Study

“…Now for calculating ⟨q 4 ⟩, if we consider only n (≤4) water neighbors that are within the first four neighbors, then the ⟨q 4 ⟩ value does not significantly decrease with GdmCl concentration (see blue line in Figure 10). In this case, when n < 4, we have used proper normalization (see Bandyopadhyay et al 60 for details). So, the rapid decrease in ⟨q 4 ⟩ as a function of GdmCl concentration that was observed earlier 51 should not be attributed to breaking of tetrahedral network of water but, on the contrary, it is due to selection of wrong water neighbors.…”

Non-thermal effects of microwave in sodium chloride aqueous solution: Insights from molecular dynamics simulations

“…The values of q 4 is decline with the field strength increase and less than values of pure water [69] under the high intensities fields from the Fig. 3.…”

“…It quantifies the tetrahedral order of the system by measuring the deviation from the ideal tetrahedral structure. The q 4 ∈ (0,1] [69]. Our previous experiment indicated the dynamics of these structures do not change monotonically with microwave frequency.…”

“…From tetrahedral structure of water perspective (Scheme 2), the average value of the tetrahedral order parameter (q 4 ) averaged over all the molecules N is then defined as [68,69]:…”