A Discrete Ion Stochastic Continuum Overdamped Solvent Algorithm for Modeling Electrolytes

TL;DR

This paper introduces a mesoscale simulation method for electrolytes that combines particle-based and continuum approaches, accurately capturing electrostatic and hydrodynamic interactions with validation against classical theories.

Contribution

It extends the Fluctuating Immersed Boundary approach with novel electrostatic and short-range force treatments for electrolyte modeling.

Findings

Accurately reproduces Debye-Hückel ion correlation functions.

Matches Debye-Hückel-Onsager conductivity predictions.

Validates the method against strong electric field effects.

Abstract

In this paper we develop a methodology for the mesoscale simulation of strong electrolytes. The methodology is an extension of the Fluctuating Immersed Boundary (FIB) approach that treats a solute as discrete Lagrangian particles that interact with Eulerian hydrodynamic and electrostatic fields. In both cases the Immersed Boundary (IB) method of Peskin is used for particle-field coupling. Hydrodynamic interactions are taken to be overdamped, with thermal noise incorporated using the fluctuating Stokes equation, including a "dry diffusion" Brownian motion to account for scales not resolved by the coarse-grained model of the solvent. Long range electrostatic interactions are computed by solving the Poisson equation, with short range corrections included using a novel immersed-boundary variant of the classical Particle-Particle Particle-Mesh (P3M) technique. Also included is a short range repulsive force based on the Weeks-Chandler-Andersen (WCA) potential. The new methodology is validated by comparison to Debye-H{\"u}ckel theory for ion-ion pair correlation functions, and Debye-H{\"u}ckel-Onsager theory for conductivity, including the Wein effect for strong electric fields. In each case good agreement is observed, provided that hydrodynamic interactions at the typical ion-ion separation are resolved by the fluid grid.