Density fluctuations in an electrolyte from generalized Debye-Huckel theory

Near-critical thermodynamics in the hard-sphere (1,1) electrolyte is well described, at a classical level, by Debye-Huckel (DH) theory with (+,-) ion pairing and dipolar-pair-ionic-fluid coupling. But DH-based theories do not address density fluctuations. Here density correlations are obtained by functional differentiation of DH theory generalized to nonuniform densities of various species. The correlation length xi diverges universally at low density rho as (T rho)(-1/4) (correcting the generalized mean. spherical approximation). When rho = rho(c) one has xi similar or equal to xi(0)(+)/t(1/2) as t = (T - T-c)/T-c --> 0+, where the amplitudes xi(0)(+) compare informatively with experimental data.