Temperature-dependence of time-dependent friction and electric field fluctuations

Sivaprasad, K. R.; Prasad, V.; Devi, Kavita; Tembe, B. L.

doi:10.1007/bf02840763

Cited by 5 publications

(3 citation statements)

References 26 publications

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“…They found that the cross-terms are not zero. Later studies carried out by Sridhar et al using a different water potential came to similar conclusions. Recently, Chong and Hirata have considered a further extension of the theory of ion mobility in a dipolar solvent in which the cross-terms are not neglected.…”

Section: The Friction On An Ionmentioning

confidence: 53%

Friction Coefficients of Ions in Aqueous Solution at 25 °C

1998

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The diffusion coefficients of ions and of uncharged solutes in aqueous solution at 25 °C and at infinite dilution are studied by computer simulation using the SPC/E model for water and solute−water potentials employed in previous work (Koneshan, S.; et al. J. Phys. Chem. 1998, 102, 4193−4204). The mobilities of the ions calculated from the diffusion coefficients pass through a maximum as a function of ion size, with distinct curves and maximums for positive and negative ions in qualitative agreement with experiment. We aim to understand this at a microscopic level in terms of theoretical studies of the friction coefficient ζ, which is related to diffusion coefficient by the Stokes−Einstein relation. This provides one method of calculating ζ, but it can also be obtained in principle from the random force autocorrelation function which is the starting point of molecular theories of the friction. Molecular and continuum theories divide the friction into hydrodynamic and dielectric components calculated in different ways on the basis of certain approximations that are tested in this paper. The two methods of determining ζ give consistent results in simulations of large ions or uncharged solutes but differ by a factor of nearly 1.5 for smaller ions. This is attributed to the assumption, in our simulations and in some molecular theories, that the random force autocorrelation function of a moving ion can be approximated by the total force autocorrelation function of a fixed ion but the observed trends in ζ with ion size are unchanged. Three different separations of the force autocorrelation function are studied; namely, partitioning this into (a) electrostatic and Lennard-Jones forces (b) hard and soft forces, and (c) forces arising from the first shell and more distant forces. The cross-terms are found to be significant in all cases, and the contributions of the sum of the soft term and the cross-terms, which are of opposite sign, to the total friction in the hard−soft separation, is small for all the ions (large and small). This suggests that dielectric friction calculated using this separation, with the neglect of cross-terms, is less accurate than previously supposed and the success of these theories is due to a cancellation of errors in the approximations. This is supported by recent a theoretical study of Chong and Hirata (Chong, C.; Hirata, F. J. Chem. Phys. 1998, 108, 739) which evaluates the cross-terms. A phenomenological theory due to Chen and Adelman (Chen, J. H.; Adelman, S. A. J. Chem. Phys. 1980, 72, 2819) calculates the friction in terms of effective hydrodynamic and dielectric radii for the ions (cf. solventberg picture) and predicts low dielectric friction for large ions and small strongly solvated ions. This also agrees qualitatively with our simulations but a complete molecular theory, applicable to positive and negative ions in hydrogen-bonded solvents such as water, has yet to be developed.

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Section: The Friction On An Ionmentioning

confidence: 53%

Friction Coefficients of Ions in Aqueous Solution at 25 °C

1998

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“…Later Tembe and coworkers [32,33] and Koneshan et al [34] also confirmed that cross terms cannot be neglected.…”

Section: Introductionmentioning

confidence: 92%

A mode-coupling theory analysis of the observed diffusion anomaly in aqueous polyatomic ions

Banerjee

Bagchi

2017

The Journal of Chemical Physics

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In contrast to simple monatomic alkali and halide ions, complex polyatomic ions such as nitrate, acetate, nitrite, and chlorate have not been studied in any great detail. Experiments have shown that diffusion of polyatomic ions exhibits many remarkable anomalies; notable among them is the fact that polyatomic ions with similar size show large difference in their diffusivity values. This fact has drawn relatively little interest in scientific discussions. We show here that a mode-coupling theory can provide a physically meaningful interpretation of the anomalous diffusivity of polyatomic ions in water, by including the contribution of rotational jumps on translational friction. The two systems discussed here, namely, aqueous nitrate ion and aqueous acetate ion, although have similar ionic radii, exhibit largely different diffusivity values due to the differences in the rate of their rotational jump motions. We have further verified the mode-coupling theory formalism by comparing it with experimental and simulation results that agree well with the theoretical prediction.

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“…Wolynes in his attempt to formulate a microscopic theory of dielectric friction identified the term ζ HH as the Stokes friction and ζ SS as the dielectric friction and neglected the other two terms. 7,27 Later by theoretical approach 6 and by computer simulations, 8,16,17,[31][32][33][34] several studies confirmed that the cross terms cannot be fully neglected.…”

Section: Microscopic Theories For Monatomic Ionsmentioning

confidence: 97%

Ions’ motion in water

Banerjee

Bagchi

2019

The Journal of Chemical Physics

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Over the decades, a great deal of attention has been focused on the solvation and transport properties of small rigid monatomic ions such as Na + , K + , Li + , Cl − , and Br − due to their importance in physical chemistry. Much less attention has been devoted to polyatomic ions although many polyatomic ions (such as nitrate, acetate, sulfate, and ammonium) are of great importance in biological and chemical processes. While the translational diffusion of smaller rigid ions shows the remarkable nonmonotonic dependence on inverse ion size (known as the "breakdown of Walden product"), the intermediate-to large-sized polyatomic ions (such as nitrate, acetate, and sulfate) exhibit different anomalies pointed out only recently. In this Perspective article, we provide an overview of how rotational diffusion and translational diffusion of these ions themselves are coupled to translational and rotational motions of water molecules. We discuss how diffusion of polyatomic ions is different from that of monatomic ions due to the rotational self-motion of the former that enhances diffusion in specific cases because of symmetry. While a continuum hydrodynamic model fails to describe the motion of polyatomic ions, we discuss how a mode-coupling theory approach can capture many aspects of this coupling between the solute ion and solvent water. We discuss how ionic mobility in water and other dipolar solvents are intimately connected to the dipolar solvation dynamics, in particular to its ultrafast component. We point out how the usual thinking on the relation between the diffusion and entropy needs to be modified in the case of ion diffusion.

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Temperature-dependence of time-dependent friction and electric field fluctuations

Cited by 5 publications

References 26 publications

Friction Coefficients of Ions in Aqueous Solution at 25 °C

Friction Coefficients of Ions in Aqueous Solution at 25 °C

A mode-coupling theory analysis of the observed diffusion anomaly in aqueous polyatomic ions

Ions’ motion in water

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