Coulombic interaction ionic fluids

The bare Coulombic interaction (p = 1) and interactions of charges with rotating dipoles (p = 4) do not fall into this class, and it has been argued for a long time [30] that in this case one expects analytical ( classical ) behavior. This implies that the system can be described by a mean-field Hamiltonian, in which the interaction of a particle is ascribed to the mean field of all other particles, thus ignoring local fluctuations [10]. In real ionic fluids the... 

Most work has dealt with the RPM as a generic model for ionic criticality. MC data suggest that the replacement of the solvent s dielectric continuum by discrete solvent molecules does not change the principal topology of the phase diagram. This ensures that the simple RPM covers the major features of real ionic fluids, at least in cases where Coulombic interactions prevail. 

We turn now to theories of ionic criticality that encompass nonclassical phenomena. Mean-field-like criticality of ionic fluids was debated in 1972 [30] and according to a remark by Friedman in this discussion [69], this subject seems to have attracted attention in 1963. Arguments in favor of a mean-field criticality of ionic systems, at least in part, seem to go back to the work of Kac et al. [288], who showed in 1962 that in D = 1 classical van der Waals behavior is obtained for a potential of the form ionic fluids with attractive and repulsive Coulombic interactions have little in common with the simple Kac fluid. 

Denesyuk, N.A., Weeks, J.D. A new approach for efficient simulation of Coulomb interactions in ionic fluids. J. Chem. Phys. 2008,128, 124109. 

Here cr is the collision diameter and e is the depth of the potential well at the minimum of zz(r). For molecules we often use combinations of atomic pair potentials, adding several body potentials that describe bending or torsion when needed. For dipolar fluids we have to add dipole-dipole interactions (or, in a more sophisticated description. Coulomb interactions between partial charges on the atoms) and for ionic solutions also Coulomb interactions between the ionic charges. 

Figure 14 shows the three structure functions for CaF2 at 1773°K calculated using one set of ionic radii (a+ = 1.94 A, a = 2.18 A) taken from reference(27). As can be noted, the first minimum in the Ca-F interaction function falls at a value of k equal to the one where t e first maximum of the Ca-Ca and F-F interactions are located ( 2.2 A ). This condition is typical of fluids with strong coulombic interaction in fact according to equation (21) the charge-charge structure function S (k) will show a sharp peak r, 9.9 due to the reinforcement of the three structure func-... 

Following the success of Chan s simple proposition, and given the accuracy of SAFT in modelling the properties of non-ionic fluids, it is a natural extension to combine a treatment of the solvent and other non-Coulombic terms using SAFT with a contribution to treat charge-charge interactions from a primitive model theory. The Helmholtz energy of the electrolyte solution is usually therefore written as... 

For convenience, the potential energy of interaction, aside from the coulombic term, was chosen to be the same for all particles, being a rough approximation to that appropriate to molten KCl. Its form was that recommended by Woodcock ( ). The symmetry of the potential plus the absence of ionic polarization terms means that the results are not specific to any real salt but rather pertain only to this model. On the other hand, the main results are meant to refer to the properties associated with dense ionic fluids in general and not to unique properties associated with various anomalies in the... 

The simple fluids considered above are all characterized by short range interactions where the second virial coefficient B2 ( ) is finite. In the case of ionic systems the Coulomb energy of two point charges ij, and qj separated by a distance r reads... 

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