The quantity ψ O can be simply substituted into the expression in Equation , a modification that is explored at length in Kudlay, et al. At reasonable concentrations, this result has significant implications on phase behavior, in particular leading to a partitioning of salt out of the coacervate phase. We note that this approach does not modify the diagrams considered by the cluster expansion, and still considers only the ring diagrams. This is a general feature of the RPA approximation, even outside the context of electrostatics. For example, using ψ(k) = v represents an interaction of u c,α,γ (r) = vδ(r), which then leads immediately to the Edwards result for the polymer solution free energy. This approach is still an improvement, of course, since it no longer neglects the effect of excluded volume that would otherwise be in the f 0 -bonds, yet there are other possible approaches.