Density Fluctuations in an Electrolyte from Generalized Debye-Hückel Theory

Near-critical thermodynamics in the hard-sphere (1, 1) electrolyte is well described, at a classical level, by Debye-H\"uckel (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 diverges universally at low density as (T) ^-1/4 (correcting the generalized mean-spherical approximation). When 0ex{0ex}=0ex{0ex}₂ one has ₀^+/t^1/2 as t (T-T₂) /T₂0+, where the amplitudes ₀^+ compare informatively with experimental data.