Dielectric constant and density of aqueous alkali halide solutions by molecular dynamics: A force field assessment

Abstract

The concentration dependence of the dielectric constant and the density of 11 aqueous alkali halide solutions (LiCl, NaCl, KCl, RbCl, CsCl, LiI, NaI, KI, CsI, KF, and CsF) is investigated by molecular simulation. Predictions using eight non-polarizable ion force fields combined with the TIP4P/ε water model are compared to experimental data. The influence of the water model and the temperature on the results for the NaCl brine are also addressed. The TIP4P/ε water model improves the accuracy of dielectric constant predictions compared to the SPC/E water model. The solution density is predicted well by most ion models. Almost all ion force fields qualitatively capture the decline of the dielectric constant with the increase of concentration for all solutions and with the increase of temperature for NaCl brine. However, the sampled dielectric constant is mostly in poor quantitative agreement with experimental data. These results are related to the microscopic solution structure, ion pairing, and ultimately the force field parameters. Ion force fields with excessive contact ion pairing and precipitation below the experimental solubility limit generally yield higher dielectric constant values. An adequate reproduction of the experimental solubility limit should therefore be a prerequisite for further investigations of the dielectric constant of aqueous electrolyte solutions by molecular simulation.

Molecular dynamics simulation of lithium fluoride in aqueous solutions at different temperatures 300 K – 360 K

“…We notice that our value of the simulated dielectric constant using SPC/E is relatively small compared to that found experimentally for pure water (ε = 78.5). However, our results are in good agreement with other studies [30][31][32]. Table 3.…”

SAMPL7 Host–Guest Challenge Overview: assessing the reliability of polarizable and non-polarizable methods for binding free energy calculations

“…Fixed point charge water models are limited in some ways by their use of the same partial charges to empirically fit the potential energy landscape and dipole moment, two distinct water properties [44,45]. Inevitably, the choice in water model (many listed in [46,47]) may also dictate the accuracy in (a) solvation, (b) dielectric constant, and (c) dipole moment [44], and affect ionic behavior along with many other properties.…”

“…Fixed point charge water models are limited in some ways by their use of the same partial charges to empirically fit the potential energy landscape and dipole moment, two distinct water properties [44,45]. Inevitably, the choice in water model (many listed in [46,47]) may also dictate the accuracy in (a) solvation, (b) dielectric constant, and (c) dipole moment [44], and affect ionic behavior along with many other properties. Previous work in the Gilson lab indicated that even fixed-charge water models can vary dramatically in water placement and orientation around hosts as well as in thermodynamic properties like the enthalpy of binding [48,49], and it seems likely that polarizable models may exhibit even larger differences.…”

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“…In case of Ewald summation, the summation of partial charges to a molecular dipole moment µ i is carried out for each molecule. If a mixture contains ions, which carry a permanent charge, they affect the dielectric constant only through their interactions that alter the orientation of solvent molecules [34]. Fig.…”