Field-theoretic description of ionic crystallization in the restricted primitive model

TL;DR

This paper uses a field-theoretic approach to study ionic crystallization in the restricted primitive model, revealing that fluctuations eliminate the continuous transition line and induce a first-order transition consistent with simulations.

Contribution

It introduces a fluctuation analysis within a $ ext{phi}^6$ theory framework, showing the disappearance of the mean-field $ ext{lambda}$-line and the emergence of a fluctuation-induced first-order transition.

Findings

Fluctuations remove the mean-field $ ext{lambda}$-line.

A first-order transition to charge-ordered phase is induced by fluctuations.

The charge-ordered phase corresponds to ionic crystal formation.

Abstract

Effects of charge-density fluctuations on a phase behavior of the restricted primitive model (RPM) are studied within a field-theoretic formalism. We focus on a $\lambda$-line of continuous transitions between charge-ordered and charge-disordered phases that is observed in several mean-field (MF) theories, but is absent in simulation results. In our study the RPM is reduced to a $\phi^6$ theory, and a fluctuation contribution to a grand thermodynamic potential is obtained by generalizing the Brazovskii approach. We find that in a presence of fluctuations the $\lambda$-line disappears. Instead, a fluctuation-induced first-order transition to a charge-ordered phase appears in the same region of a phase diagram, where the liquid -- ionic-crystal transition is obtained in simulations. Our results indicate that the charge-ordered phase should be identified with an ionic crystal.