Thermal and structural properties of ionic fluids

TL;DR

This study demonstrates that the phase behavior and structure of ionic fluids are primarily determined by valency dependence rather than the long-range nature of electrostatic interactions, as shown through Monte Carlo simulations with short-ranged potentials.

Contribution

The paper shows that short-ranged potentials with smooth cut-offs can replicate the phase behavior and structure of long-ranged electrostatic interactions in ionic fluids.

Findings

Short-ranged potentials with smooth cut-offs reproduce the phase behavior of long-range models.

Sharply cut off potentials show dependence on cut-off radius affecting phase behavior.

Short-ranged models with smooth cut-offs fulfill the Stillinger-Lovett screening property.

Abstract

The electrostatic interaction in ionic fluids is well-known to give rise to a characteristic phase behavior and structure. Sometimes its long range is proposed to single out the electrostatic potential over other interactions with shorter ranges. Here the importance of the range for the phase behavior and the structure of ionic fluids is investigated by means of grandcanonical Monte Carlo simulations of the lattice restricted primitive model (LRPM). The long-ranged electrostatic interaction is compared to various types of short-ranged potentials obtained by sharp and/or smooth cut-off schemes. Sharply cut off electrostatic potentials are found to lead to a strong dependence of the phase behavior and the structure on the cut-off radius. However, when combined with a suitable additional smooth cut-off, the short-ranged LRPM is found to exhibit quantitatively the same phase behavior and structure as the conventional long-ranged LRPM. Moreover, the Stillinger-Lovett perfect screening property, which is well-known to be generated by the long-ranged electrostatic potential, is also fulfilled by short-ranged LRPMs with smooth cut-offs. By showing that the characteristic phase behavior and structure of ionic fluids can also be found in systems with short-ranged potentials, one can conclude that the decisive property of the electrostatic potential in ionic fluids is not the long range but rather the valency dependence.