Exact equations and the theory of liquids

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Abstract
It has been shown that a formal small parameter λ can be introduced into exact equations obtained earlier for systems of charged particles [1, 2] exactly in the same manner as for systems of uncharged particles. Expansion in a series in λ makes it possible to obtain a generalized hypernetted chain approximation (HNC) for charged particles. The solution of the HNC approximation was examined for the hard charged spheres model over a wide range of parameters corresponding to aqueous electrolytes. Slowly attenuating oscillations (in-phase and out-of-phase) have been observed at high densities. Thus, as the density rises, the correlation radius (equal to the Debye radius in dilute solutions) first decreases and then starts rising again. In so doing, the steady decrease in the potential typical of dilute systems changes into an oscillating behaviour and the potential may become negative. The problem of the divergence of the HNC solution at moderate temperatures is discussed.