Accelerated simulation method for charge regulation effects

TL;DR

This paper introduces an efficient Monte Carlo method for simulating charge regulation effects in complex systems, enabling accurate modeling of ionizable groups with linear computational scaling and implementation in LAMMPS.

Contribution

The paper presents a new hybrid MD/CR-MC simulation method with open-source implementation that accurately models charge redistribution in large systems, improving computational efficiency.

Findings

Quantified charge regulation effects on polyelectrolyte transitions.

Analyzed interactions between oppositely charged nanoparticles.

Achieved linear scaling with the number of ionizable groups.

Abstract

The net charge of solvated entities, ranging from polyelectrolytes and biomolecules to charged nanoparticles and membranes, depends on the local dissociation equilibrium of individual ionizable groups. Incorporation of this phenomenon, \emph{charge regulation}, in theoretical and computational models requires dynamic, configuration-dependent recalculation of surface charges and is therefore typically approximated by assuming constant net charge on particles. Various computational methods exist that address this. We present an alternative, particularly efficient charge regulation Monte Carlo method (CR-MC), which explicitly models the redistribution of individual charges and accurately samples the correct grand-canonical charge distribution. In addition, we provide an open-source implementation in the LAMMPS molecular dynamics (MD) simulation package, resulting in a hybrid MD/CR-MC simulation method. This implementation is designed to handle a wide range of implicit-solvent systems that model discreet ionizable groups or surface sites. The computational cost of the method scales linearly with the number of ionizable groups, thereby allowing accurate simulations of systems containing thousands of individual ionizable sites. By matter of illustration, we use the CR-MC method to quantify the effects of charge regulation on the nature of the polyelectrolyte coil--globule transition and on the effective interaction between oppositely charged nanoparticles.