Microwave dielectric properties of aqueous solutions of potassium and cesium fluorides

112

177

The structure of aqueous LiCl, NaCl, KCl, CsCl, KF, and NaI solutions is calculated by molecular dynamics (MD) simulations of the frequently employed Dang force-field in SPC/E water. By using liquid state theory, we integrate the structure to obtain the electrolytes' osmotic coefficient phi and systematically investigate force-field quality and structural consequences to ion-specific bulk thermodynamics. The osmotic coefficients phi(chi) calculated from the exact compressibility route for the cation-Cl(-) force-fields match experiments for concentrations rho approximately < 2M, while NaI and KF parameters fail. Comparison of phi(chi) with phi(v) from the virial route, which relies on the pair potential approximation, shows that many-body effects become important for all salts above rho approximately 0.5M. They can be efficiently corrected, however, by employing a salt-type and rho-dependent dielectric constant epsilon(rho), generalizing previous observations on NaCl only. For physiological concentrations, rho approximately < 0.5M, the specific osmotic behavior is found to be determined by the short-ranged cation-anion pair potential only and is strongly related to the second virial coefficient of the latter. Presented methods and findings, based on simple integrations over the electrolyte structure, enable efficient MD force-field refinement by direct benchmarking to the sensitive electrolyte thermodynamics, instead to noncollective, single ion properties.

Section: B Water Dielectric Constantsupporting

confidence: 78%

Structure-thermodynamics relation of electrolyte solutions

Kalcher

Dzubiella

2009

112

177

“…The data is taken from Ref. [47], and the solid curve is plotted by adjusting the only fit parameter, a = 3.2 Å.…”

Section: Discussionmentioning

confidence: 99%

“…where ε ∞ is the dielectric constant in the high frequency limit, ε s is the static dielectric constant (that is of interest to us), τ is the dielectric relaxation time, α is the relaxation time distribution parameter, and σ dc is the DC conductivity. In the experiments we review here [45][46][47], the dielectric response was measured in frequencies ranging from 45 MHz to 25 GHz, and ε s was obtained as a fitting parameter from Eq. ( 42).…”

Section: Comparison To Experimentsmentioning

confidence: 99%

See 1 more Smart Citation

Dielectric constant of ionic solutions: Combined effects of correlations and excluded volume

Adar

Markovich

Levy

et al. 2018

The dielectric constant of ionic solutions is known to reduce with increasing ionic concentrations. However, the origin of this effect has not been thoroughly explored. In this paper, we study two such possible sources: long-range Coulombic correlations and solvent excluded-volume. Correlations originate from fluctuations of the electrostatic potential beyond the mean-field Poisson-Boltzmann theory, evaluated by employing a field-theoretical loop expansion of the free energy. The solvent excluded-volume, on the other hand, stems from the finite ion size, accounted for via a lattice-gas model. We show that both correlations and excluded volume are required in order to capture the important features of the dielectric behavior. For highly polar solvents, such as water, the dielectric constant is given by the product of the solvent volume fraction and a concentration-dependent susceptibility per volume fraction. The available solvent volume decreases as a function of ionic strength due the increasing volume fraction of ions. A similar decrease occurs for the susceptibility due to the correlations between the ions and solvent, reducing the dielectric response even further. Our predictions for the dielectric constant fit well with experiments for a wide range of concentrations for different salts in different temperatures, using a single fit parameter related to the ion size.

“…4 Despite its significance, the dielectric constant of even the simplest aqueous monovalent salt solutions is poorly studied by experiment and sufficiently available only for 11 of the 20 alkali halide brines. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] In fact, the dielectric constant is not directly measurable in the laboratory. 20 It has to be extrapolated from the frequency-dependent dielectric constant in a non-trivial procedure, which requires elaborate measurement instruments, dielectric relaxation models, and a complex estimation of model parameters.…”

Section: Introductionmentioning

confidence: 99%

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

Šarić

Kohns

Vrabec

2020

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.