Distribution function Weeks-Chandler-Andersen

An elegant theory to go beyond the hard-sphere cavity was presented by Pratt and Chandler [17], where the attractive part of the solute-water interaction was treated perturbatively (in the spirit of the Weeks-Chandler-Andersen (WCA) theory [18]). The central quantities in the Pratt-Chandler theory are two radial distribution functions, gAw f) that give, respectively, the... 

Fig. 1. Like and unlike pair distribution functions at concentration 1.968 M for 1-1 ionic solution at 298°K, with ionic diameter R = 4.25 A and solvent dielectric constant e = 78.5. The points (0,D) represent Monte Carlo calculations for 200 ions [J. P. Valleau, private communication D. N. Card and J. P. Valleau, /. Chem. Phys. 52, 6232 (1970)]. The curves ctmnpare the LIN+ +AB2 and QUAD+ 2 results of the text, along with the EXP approximation of Andersen, Chandler, and Weeks. Tlie lower set of results is for g++ and g the upper set is for g+- and g +.

Points 1 and 2 can be incorporated straightforwardly using the ideas presented earlier in this chapter. For example, we could use the analytic Percus-Yevick equations of state for hard spheres (Eqs. 47a and b) or the Carnahan-Starling equation of state (Eq. 49) for p. Furthermore, we could use the hard-sphere radial distribution function obtained numerically from one of the integral equations or even that calculated from computer simulation. Points 3 and 4 are less straightforward and represent contributions that were made around 1970 by Barker and Henderson (1976) and by Weeks, Chandler and Andersen (1971). The results of these two approaches are comparable and are illustrated in Figs. 10 and 11 and Table 3. 

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