Complete phase behavior of the symmetrical colloidal electrolyte

Caballero, José B.; Noya, Eva G.; Vega, Carlos

doi:10.1063/1.2816707

Cited by 9 publications

(15 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This is so because the interaction between charged particles is screened by the presence of an ionic atmosphere due to the counter ions of the colloids. In fact, when this screening is incorporated in the potential with a Yukawa type model, the CuAu structure was found to be stable in a thermodynamic region between the CsCl and the tetragonal structure [56,281].…”

Section: Phase Diagram For a Primitive Model Of Electrolytementioning

confidence: 99%

Determination of phase diagrams via computer simulation: methodology and applications to water, electrolytes and proteins

Vega¹,

Sanz

Abascal

et al. 2008

J. Phys.: Condens. Matter

278

452

View full text Add to dashboard Cite

Abstract. In this review we focus on the determination of phase diagrams by computer simulation with particular attention to the fluid-solid and solid-solid equilibria. The methodology to compute the free energy of solid phases will be discussed. In particular, the Einstein crystal and Einstein molecule methodologies are described in a comprehensive way. It is shown that both methodologies yield the same free energies and that free energies of solid phases present noticeable finite size effects. In fact this is the case for hard spheres in the solid phase. Finite size corrections can be introduced, although in an approximate way, to correct for the dependence of the free energy on the size of the system. The computation of free energies of solid phases can be extended to molecular fluids. The procedure to compute free energies of solid phases of water (ices) will be described in detail. The free energies of ices Ih, II, III, IV, V, VI, VII, VIII, IX, XI and XII will be presented for the SPC/E and TIP4P models of water. Initial coexistence points leading to the determination of the phase diagram of water for these two models will be provided. Other methods to estimate the melting point of a solid, as the direct fluid-solid coexistence or simulations of the free surface of the solid will be discussed. It will be shown that the melting points of ice Ih for several water models, obtained from free energy calculations, direct coexistence simulations and free surface simulations, agree within their statistical uncertainty. Phase diagram calculations can indeed help to improve potential models of molecular fluids. For instance, for water, the potential model TIP4P/2005 can be regarded as an improved version of TIP4P. Here we will review some recent work on the phase diagram of the simplest ionic model, the restricted primitive model. Although originally devised to describe ionic liquids, the model is becoming quite popular to describe the behaviour of charged colloids. Besides the possibility of obtaining fluid-solid equilibria for simple protein models will be discussed. In these primitive models, the protein is described by a spherical potential with certain anisotropic bonding sites (patchy sites).

show abstract

Section: Phase Diagram For a Primitive Model Of Electrolytementioning

confidence: 99%

Determination of phase diagrams via computer simulation: methodology and applications to water, electrolytes and proteins

Vega¹,

Sanz

Abascal

et al. 2008

J. Phys.: Condens. Matter

278

452

View full text Add to dashboard Cite

show abstract

“…3,9 Using this technique, the free energy of several atomic and molecular solids has been computed. 4,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36 Quite recently a new method to compute the free energies of solids which was denoted as "the Einstein molecule" approach has been proposed. 37,38 This method consists of a slight modification of the Einstein crystal method.…”

Section: Introductionmentioning

confidence: 99%

Computing the free energy of molecular solids by the Einstein molecule approach: Ices XIII and XIV, hard-dumbbells and a patchy model of proteins

Noya

Conde²,

Vega³

2008

The Journal of Chemical Physics

View full text Add to dashboard Cite

The recently proposed Einstein molecule approach is extended to compute the free energy of molecular solids. This method is a variant of the Einstein crystal method of Frenkel and Ladd[J.Chem. Phys. 81, 3188 (1984)]. In order to show its applicability, we have computed the free energy of a hard-dumbbells solid, of two recently discovered solid phases of water, namely, ice XIII and ice XIV, where the interactions between water molecules are described by the rigid non-polarizable TIP4P/2005 model potential, and of several solid phases that are thermodynamically stable for an anisotropic patchy model with octahedral symmetry which mimics proteins. Our calculations show that both the Einstein crystal method and the Einstein molecule approach yield the same results within statistical uncertainty. In addition, we have studied in detail some subtle issues concerning the calculation of the free energy of molecular solids. First, for solids with non-cubic symmetry, we have studied the effect of the shape of the simulation box on the free energy. Our results show that the equilibrium shape of the simulation box must be used to compute the free energy in order to avoid the appearance of artificial stress in the system that will result in an increase of the free energy. In complex solids, such as the solid phases of water, another difficulty is related to the choice of the reference structure. As in some cases there is not an obvious orientation of the molecules, it is not clear how to generate the reference structure. Our results will show that, as long as the structure is not too far from the equilibrium structure, the calculated free energy is invariant to the reference structure used in the free energy calculations. Finally, the strong size dependence of the free energy of solids is also studied.

show abstract

“…(12) and (14) leads to the expected chemical equilibrium condition: μ 2 (T , n 1 , n 2 ) = 2μ 1 (T , n 1 , n 2 ).…”

Section: The "Chemical Picture"mentioning

confidence: 97%

“…9,10 This situation contrasts with the hard, impenetrable core of microscopic ions in electrolytes and ionic liquids, or of charged colloidal particles in solution, so-called "colloidal electrolytes." [11][12][13] The standard model used to describe electrolytes is the "primitive model" (PM) of oppositely charged hard spheres in a dielectric continuum of permittivity representing the polar solvent. 14 a) arash.nikoubashman@tuwien.ac.at.…”

Section: Introductionmentioning

confidence: 99%

Mean-field theory of the phase diagram of ultrasoft, oppositely charged polyions in solution

Nikoubashman

Hansen

Kahl

2012

The Journal of Chemical Physics

View full text Add to dashboard Cite

We investigate the phase separation of the "ultrasoft restricted primitive model" (URPM), a coarse-grained representation of oppositely charged, interpenetrating polyelectrolytes, within a mean-field description based on the "chemical picture." The latter distinguishes between free ions and dimers of oppositely charged ions (Bjerrum pairs) which are in chemical equilibrium governed by a law of mass action. Interactions between ions, and between ions and dimers are treated within linearized Poisson-Boltzmann theory, at four levels of approximation corresponding to increasingly refined descriptions of the interactions. The URPM is found to phase separate into a dilute phase of dimers, and a concentrated phase of mostly free (unpaired) ions below a critical temperature T(c). The phase diagram differs, however, considerably from the predictions of recent simulations; T(c) is about three times higher, and the critical density is much lower than the corresponding simulation data [D. Coslovich, J. P. Hansen, and G. Kahl, Soft Matter 7, 1690 (2011)]. Possible reasons for this unexpected failure of mean-field theory are discussed. The Kirkwood line, separating the regimes of monotonically decaying and damped oscillatory decay of the charge-charge correlation function at large distances is determined within the random phase approximation.

show abstract

Complete phase behavior of the symmetrical colloidal electrolyte

Cited by 9 publications

References 25 publications

Determination of phase diagrams via computer simulation: methodology and applications to water, electrolytes and proteins

Determination of phase diagrams via computer simulation: methodology and applications to water, electrolytes and proteins

Computing the free energy of molecular solids by the Einstein molecule approach: Ices XIII and XIV, hard-dumbbells and a patchy model of proteins

Mean-field theory of the phase diagram of ultrasoft, oppositely charged polyions in solution

Contact Info

Product

Resources

About