Ionic criticality : an exactly soluble model

TL;DR

This paper introduces an exactly solvable model for ionic fluid criticality, revealing how charge asymmetry influences correlation lengths and violates classical screening rules at critical points.

Contribution

It presents a novel exactly soluble spherical model for ionic criticality, highlighting the effects of charge asymmetry on correlation lengths and screening behavior.

Findings

Charge symmetry leads to exponential Debye screening at criticality.

Charge asymmetry causes divergence of charge and density correlation lengths.

The Stillinger-Lovett rule is violated at criticality in asymmetric models.

Abstract

Gas-liquid criticality in ionic fluids is studied in exactly soluble spherical models that use interlaced sublattices to represent hard-core \textit{multi}component systems. Short range attractions in the uncharged fluid drive criticality but charged ions do not alter the universality class. Debye screening remains exponential \textit{at} criticality in charge-symmetric 1:1 models. However, \textit{asymmetry} couples charge and density fluctuations in a direct manner: the charge correlation length then diverges precisely as the density correlation length and the Stillinger-Lovett rule is violated \textit{at} criticality.