An effective pair potential for dipolar fluids

Woodward, Clifford E.; Nordholm, Sture

doi:10.1080/00268978400101711

Cited by 36 publications

(14 citation statements)

References 27 publications

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“…Even the simpler model of dipolar fluids (the dipolar hard-sphere system) shows a quite complex behaviour. By averaging over the orientations the dipolar interaction a Lennard-Jones-like effective potential is obtained [4,5], so it was conjectured that the dipolar hard-sphere would have a gas-liquid phase transition similar to the observed in simple fluids. However the seminal N V T computer simulation study by Weis and Levesque [6,7] showed no indication of a liquid-vapour transition.…”

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confidence: 99%

Finite-size scaling study of the liquid–vapour critical point of dipolar square-well fluids

2009

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confidence: 99%

Finite-size scaling study of the liquid–vapour critical point of dipolar square-well fluids

2009

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“…11,67 From a computational point of view, short-range many-body interactions could be easier to treat than long-range two-body interactions, in some situations. To this end, the two-body interaction potential can be developed in a number of ways beyond the leadingorder term used in this work, [33][34][35][36][37][38][39][40]45 and the three-body Axilrod-Teller potential can be retained as the chain-forming interaction. The prospect of moving to four-body interactions is not appealing.…”

Section: Discussionmentioning

confidence: 99%

“…Many attempts have been made to determine an effective two-body potential by taking angular averages of the Boltzmann distribution. [33][34][35][36][37][38][39][40] If the RDF is available, 41 then one can seek a unique density-dependent effective pair potential 42 by using iterative Boltzmann inversion starting from the potential of mean force −k B T ln g(r), 43,44 or by inverting the Ornstein-Zernike equation. 45 A different approach is taken here, based on a model system with two-body −r −6 attractions and three-body AT interactions -with the aforementioned temperature-dependent coefficientscomplemented by a soft-sphere repulsion.…”

Section: Introductionmentioning

confidence: 99%

Simulations of dipolar fluids using effective many-body isotropic interactions

Sindt

Camp

2015

The Journal of Chemical Physics

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The partition function of a system with pairwise-additive anisotropic dipole-dipole interactions is equal to that of a hypothetical system with many-body isotropic interactions [G. Stell, Phys. Rev. Lett. 32, 286 (1974)]. The effective many-body interactions contain n-body contributions of all orders. Each contribution is known as an expansion in terms of the particle-particle distances r, and the coefficients are temperature dependent. The leading-order two-body term is the familiar −r −6 attraction, and the leading-order three-body term is equivalent to the Axilrod-Teller interaction. In this work, a fluid of particles with the leading-order two-body and three-body interactions is compared to an equivalent dipolar soft-sphere fluid. Molecular simulations are used to determine the conditions under which the effective many-body interactions reproduce the fluid-phase structures of the dipolar system. The effective many-body interaction works well at moderately high temperatures, but fails at low temperatures where particle chaining is expected to occur. It is shown that an adjustment of the coefficients of the two-body and three-body terms leads to a good description of the structure of the dipolar fluid even in the chaining regime, due primarily to the ground-state linear configuration of the three-body Axilrod-Teller interaction. The vapor-liquid phase diagrams of systems with different Axilrod-Teller contributions are determined. As the strength of the three-body interaction is increased, the critical temperature and density both decrease, and disappear completely above a threshold strength, where chaining eventually suppresses the condensation transition.

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“…This adds significant complication to the surface tension problem. Following a series of earlier studies stretching from Keesom and Rushbroke through to more recent work by Woodward and Nordholm, , we shall use an effective potential method to map the dipole−dipole interaction onto an equivalent spherically symmetric form. Using a Stockmayer form for the pairwise interaction in the polar fluid, we then arrive, as discussed in an earlier note, at a modified Lennard-Jones potential where the parameters have become temperature dependent.…”

Section: Introductionmentioning

confidence: 99%

Estimation of the Surface Tension of Polar FluidsLong-Range Contributions

1998

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The theoretical prediction of the surface tension of polar fluids is considered with the focus on the long-range contributions arising due to orientational correlations among the dipoles. A set of three different methods are applied to a simple model of a polar fluid: (i) A very simple analysis is presented based on an effective dipole−dipole potential and the use of the generalized van der Waals (GvdW) density functional theory which has proven to be quite accurate for Lennard-Jones fluids. The effective dipole−dipole potential retains, in a low-order approximation, the Lennard-Jones form of the full potential but adds temperature dependence to the potential parameters. (ii) Molecular dynamics (MD) simulations provide a far more accurate account of the short-range interaction in the polar fluid but suffer from numerical difficulties associated with the need for a cutoff on the range of the interaction to which the surface tension is particularly sensitive. (iii) For this reason we introduce a hybrid MD/GvdW theory wherein the long-range contribution to the surface tension is estimated by the corresponding term in the GvdW result. Applications to the single-component fluids composed of HCl or HBr are presented. The interaction potential is taken to be of either Stockmayer form or a closely related form where the dipole moment is created by two point charges. The results show that the GvdW estimate agrees reasonably with experiment, and MD simulation and MD/GvdW calculation improves the convergence of the MD estimate by inclusion of both direct long-range interaction and indirect effects due to changes in the bulk phases.

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An effective pair potential for dipolar fluids

Cited by 36 publications

References 27 publications

Finite-size scaling study of the liquid–vapour critical point of dipolar square-well fluids

Finite-size scaling study of the liquid–vapour critical point of dipolar square-well fluids

Simulations of dipolar fluids using effective many-body isotropic interactions

Estimation of the Surface Tension of Polar FluidsLong-Range Contributions

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