| 1. |
- Hayashi, Yoshikatsu, et al.
(författare)
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Oppositely charged polyelectrolytes. Complex formation and effects of chain asymmetry
- 2004
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 108:39, s. 15266-15277
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Tidskriftsartikel (refereegranskat)abstract
- The formation of complexes in solutions of oppositely charged polyions has been studied by Monte Carlo simulations. The amount as well as the length, and thus, the absolute charge of one of the polyions have been varied. There is an increasing tendency to form large clusters as the excess of one kind of polyion decreases. When all polyions have the same length, this tendency reaches a maximum near, but off, equivalent amounts of the two types of polyions. When one kind of polyion is made shorter, the propensity to form large clusters decreases and the fluctuations in cluster charge increases. Simple free-energy expressions have been formulated on the basis of a set of simple rules that help rationalize the observations. By calculating cluster distributions in both grand canonical and canonical ensembles, it has been possible to show the extent of finite-size effects in the simulations.
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| 2. |
- Hebbeker, Pascal, et al.
(författare)
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Optimal Displacement Parameters in Monte Carlo Simulations
- 2016
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 12:4, s. 1459-1465
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Tidskriftsartikel (refereegranskat)abstract
- An adaptive algorithm optimizing single-particle translational displacement parameters in Metropolis Monte Carlo simulations is presented. The optimization is based on maximizing the mean square displacement of a trial move. It is shown that a large mean square displacement is strongly correlated with a high precision of average potential energy. The method is here demonstrated on model systems representing a Lennard-Jones fluid and a dilute polymer solution at poor solvent conditions. Our adaptive algorithm removes the need to provide values of displacement parameters in simulations, and it is easily extendable to optimize parameters of other types of trial moves.
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| 3. |
- Karlstrom, Gunnar, et al.
(författare)
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Effects of different boundary conditions on the long-range structure of polar liquids
- 2008
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Ingår i: JOURNAL OF PHYSICS-CONDENSED MATTER. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 20:49
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Konferensbidrag (refereegranskat)abstract
- The long-range order in strongly coupled dipolar systems has been studied using large-scale simulations for systems containing up to 100 000 particles. It is found that the boundary conditions used strongly influence the result. It is found that a periodic system modeled with the minimum image approximation yields an artificial order, whereas the same system described using the Ewald summation technique is slightly less long-range ordered, as compared to the results obtained from studies on a non-periodical spherical droplet. Analytical expressions together with scaling considerations suggest that dipolar systems are structured on all length scales. However, more extensive studies are needed to fully assess the impact of using different boundary conditions on the long-range structure of polar liquids.
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| 4. |
- Karlström, Gunnar, et al.
(författare)
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Dipolar Order in Molecular Fluids: I. Toward an Understanding
- 2011
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Ingår i: Journal of Statistical Physics. - : Springer Science and Business Media LLC. - 1572-9613 .- 0022-4715. ; 145:2, s. 410-417
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Tidskriftsartikel (refereegranskat)abstract
- The origin behind the dipolar order in molecular fluids is investigated by using a simple dipolar fluid and Monte Carlo simulation technique. A penalty function is employed to separately manipulate the positional and orientational structure of the fluid. By considering the distance-dependent Kirkwood function G (k), which in turn is related to the dielectric permittivity of the fluid, it is observed that both positional and orientational ordering are involved to establish dipolar order.
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| 5. |
- Karlström, Gunnar, et al.
(författare)
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Retardation effects breaking long-range orientational ordering in dipolar fluids.
- 2010
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 132:5
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Tidskriftsartikel (refereegranskat)abstract
- A strongly coupled dipolar fluid confined in a sphere has been examined by Monte Carlo simulations using a modified distance-dependent pair interaction to emulate retardation effects. The effective dipole-dipole interaction and a property closely related to Kirkwood's g-factor have been analyzed for potentials with different distances at which the retardation effects became effective. The retardation effects were found to break the otherwise long-range structural ordering occurring in strongly coupled dipolar fluids.
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| 6. |
- Karlström, Gunnar, et al.
(författare)
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Two-center potential correlations and its use to determine effective ion-ion interactions and dielectric permittivities in dipolar solvents
- 2010
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 132:8
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Tidskriftsartikel (refereegranskat)abstract
- General expressions for two-center electrostatic potential correlations and its use to determine (i) the effective interaction between simple ions in a dipolar solvent and (ii) the dielectric permittivity of the solvent are proposed. Such two-center potential correlations were determined from Monte Carlo simulations of spherically confined dipolar particles embedded in a dielectric medium described by using an image charge approximation. The deduced dielectric permittivities increased with increasing dipolar moment, and at large dipole moments the effective interaction displayed an attractive first minimum. (C) 2010 American Institute of Physics.
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| 7. |
- Linse, Per, et al.
(författare)
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Dipolar Order in Molecular Fluids: II. Molecular Influence
- 2011
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Ingår i: Journal of Statistical Physics. - : Springer Science and Business Media LLC. - 1572-9613 .- 0022-4715. ; 145:2, s. 418-440
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Tidskriftsartikel (refereegranskat)abstract
- The influence on the short-range packing in dipolar fluids by molecular shape and by additional higher order electrostatic moments has been investigated by molecular dynamic simulations. The dipole polarization was found to decrease as the particles were elongated parallel to the dipole and to increase for elongation perpendicular to the dipole, eventually forming a nematic order. The addition of a quadrupole lead to a reduction of the polarization, and the influence of an axial octupole was weaker and more complex. Both a decrease and an increase of the polarization is possible depending on the relative dipole-dipole and octupole-octupole interaction strengths and the relative direction of the symmetry axes of the moments. These observations were attributed to the different parity of a dipole and a quadrupole and the same parity of a dipole and an axial octupole under reflection. In addition, further insights into the formation of dipole polarization were obtained. Short polar and long equatorial radii and strong dipole-dipole interaction are particle properties that promote a fluid with a high dipole polarization.
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| 8. |
- Stenhammar, Joakim, et al.
(författare)
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A unified treatment of polar solvation using electrostatic fluctuations
- 2011
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 501:4-6, s. 364-368
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Tidskriftsartikel (refereegranskat)abstract
- A unified description of solvation in dielectric media characterized by a static relative permittivity e is presented. The approach is based on probability distributions representing fluctuating dipole moments and electric fields and goes beyond the traditional mean-field approach. In addition to reproducing some standard results, we present an expression for the solvation free energy of a dielectric sphere immersed in an infinite dielectric medium. Furthermore, the solvation process is analyzed in detail by decomposing the solvation free energy into its energetic and entropic contributions. (C) 2010 Elsevier B.V. All rights reserved.
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| 9. |
- Stenhammar, Joakim, et al.
(författare)
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An exact calculation of the van der Waals interaction between two spheres of classical dipolar fluid.
- 2010
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 114:42, s. 13372-13380
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Tidskriftsartikel (refereegranskat)abstract
- An exact treatment of the van der Waals interaction between two spherical dielectric bodies possessing purely classical degrees of freedom is presented. The spheres are described by multipole expansions of their fluctuating charge distributions, and the correlation between the fluctuations are taken into account using classical electrostatics and statistical mechanics. The presented approach avoids both the assumption of pairwise additivity of Hamaker theory and the implicit linear response assumption of Lifshitz theory. The resulting equations are solved numerically for D/a ≥ 0.01, where a is the radius of the spheres and D is their minimum separation, for a system with ε = 80, and the results are compared to the analytical Hamaker formula with a Hamaker constant calculated from Lifshitz theory.
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| 10. |
- Stenhammar, Joakim, et al.
(författare)
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Anisotropic electric fluctuations in polar liquids under spherical confinement
- 2011
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Ingår i: Molecular Physics. - : Informa UK Limited. - 1362-3028 .- 0026-8976. ; 109:1, s. 11-20
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Konferensbidrag (refereegranskat)abstract
- The anisotropic local electric fluctuations within a nanoscopic sphere of a polar fluid surrounded by vacuum are analysed using dielectric theory and molecular simulation. The electric fluctuations are characterized through the mean-square multipole moments (Q(l)(2)), which are related to the dielectric constant of the fluid. The results show that the fluctuations are suppressed close to the fluid boundary, with a stronger effect on the fluctuations perpendicular as compared to those parallel to the surface. Furthermore, the effect becomes weaker and more short-ranged as the order l of the fluctuating multipole moments is increased. The agreement between the results from dielectric theory and those from molecular simulations are satisfactory, in spite of the inhomogeneous density of the molecular system.
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