Dynamic and Electronic Polarization Corrections to the Dielectric Constant of Water

Abstract

The standard approach to calculating the dielectric constant from molecular dynamics (MD) simulations employs a variant of the Kirkwood–Fröhlich methodology. Many popular nonpolarizable models of water, such as TIPnP, give a reasonable agreement with the experimental value of 78. However, it has been argued in the literature that the dipole moments of these models are effective, being smaller than the real dipole of a liquid water molecule by about a factor of , or roughly . If the total or corrected dipole moment is used in calculations, the dielectric constant comes out nearly twice as large, i.e., in the range of 160, which is twice as high as the experimental value. Here we discuss possible reasons for such a discrepancy. One approach takes into account dynamic corrections due to the dependence of the dielectric response of the medium producing the reaction field on the time scale of dipole fluctuations computed in the Kirkwood–Fröhlich method. When dynamic corrections are incorporated into the computational scheme, a much better agreement with the experimental value of the dielectric constant is found when the corrected (real) dipole moment of liquid water is used. However, a formal analysis indicates that the static properties, such as dielectric constant, should not depend on dynamics. We discuss the resulting conundrum and related issues of simulations of electrostatic interactions using periodic boundary conditions in the context of our findings.

The dielectric constant: Reconciling simulation and experiment

“…However, a recent paper by Farahvash et al 15 shed some new light on this issue by comparing the performance of several popular non-polarizable water models. They observed that application of the MDEC approach (i.e.…”

“…Another issue that warrants further exploration is the effect of scaling on the dynamic dielectric response of fluids 15,48 . Indeed, it has been recently shown that, at least for some fluids, classical non-polarizable models are able to describe the dynamic response over a wide range of frequencies, provided the simulation results are scaled to match the corresponding experimental static dielectric constant 48 .…”

Systematic Optimization of Water Models Using Liquid/Vapor Surface Tension Data

“…Recent studies on electrostatic models have raised questions regarding whether the simulated dielectric constant requires post hoc corrections. , These studies posit that the effective electrostatic moments used to compute the MM interactions of ions and polar species should be reduced with respect to the physical charges used to compute electrostatic properties due to the dielectric screening caused by the electronic polarization of the medium. This implies that the dielectric constant computed from the partial charges in the force field should be increased by a correction prior to comparing with the experiment, or conversely, the experimental value should be reduced prior to making the comparison with the force field.…”

“…In ref , the authors concluded that the missing polarizability in nonpolarizable models scales the dielectric constant by a factor of 1.78. Under the assumption that the same correction factor would apply to our models, the reference dielectric constant should be reduced by a factor of 1/1.78 = 0.5618.…”

Predicting Positions of Bridging Water Molecules in Nucleic Acid–Ligand Complexes

“…Polarization has been found to lead to artifacts during MD simulations of proteins, 9,10 and methods to address this problem have been proposed. 44,45 However, it remains to be addressed for the more polar nucleic acids. From our quantum mechanics (QM) calculations, it was observed that a water molecule bridged by two polar atoms experienced an overall potential unequal to the sum of the two individual potentials (Figure 8).…”