Dipolar correlations in liquid water

Abstract

We present an analysis of the dipolar correlations in water as a function of temperature and density and in the presence of simple ionic solutes, carried out using molecular dynamics simulations and empirical potentials. We show that the dipole-dipole correlation function of the liquid exhibits sizable oscillations over nanodomains of about 1.5 nm radius, with several isosbestic points as a function of temperature; the size of the nanodomains is nearly independent on temperature and density, between 240 and 400 K and 0.9 and 1.3 g/cm(3), but it is substantially affected by the presence of solvated ions. In the same range of thermodynamic conditions, the decay time (τ) of the system dipole moment varies by a factor of about 30 and 1.5, as a function of temperature and density, respectively. At 300 K, we observed a maximum in τ as a function of density, and a corresponding shallow maximum in the tetrahedral order parameter, in a range where the diffusion coefficient, the pressure and the dielectric constant increase monotonically.

Finite field formalism for bulk electrolyte solutions

“…34 To give a sense of the dynamic contribution obtained in this work, in the limit c → 0, fluct is found to be 72 ± 3, in excellent agreement with previously computed values of the dielectric constant of SPC/E water. 11,12,[62][63][64][65] In contrast, the corresponding result for wat is 65 ± 1, i.e., roughly 10% smaller than fluct . Moreover, from Fig.…”

Long-range orientation correlation in water

“…Vortex-like structures 21,22 or collective motions 23 have been found in several molecular dynamics (MD) simulations for water, similar in form to the azimuthal orientation correlations previously proposed 12 as an explanation of the HRS results. Dipolar orientation correlations at the nm scale have also been found using density functional theory 24 and MD simulations [25][26][27] for water. These results are not inconsistent with the long-range orientation correlations in water observed by HRS, but are not conclusive since even the largest simulation box is <10 nm, much smaller that the length scale probed by the present HRS experiment.…”

Hierarchical lattice models of hydrogen-bond networks in water

“…Besides the structural correlations, it is well known that orientational correlations in water can be quite long range on the order of 1-2nm. In fact, recent atomistic simulations by Galli and co-workers examined the orientational correlations in water (such as dipolar correlations) and showed that these are longer-ranged than the density-density correlations [56]. We can examine the di-rectional correlations of the H-bonds on the Bethe and Husimi lattices using a transfer matrix approach [51].…”