Practical Considerations for Finite Concentrations Molecular Dynamics Simulations

TL;DR

This paper introduces SCOPE, an integrated workflow for molecular dynamics simulations that accurately predicts ion behavior and phase transitions in concentrated electrolytes, aligning well with experimental data.

Contribution

The study presents a novel, transferable simulation approach combining enhanced sampling, reweighting, and chemical potential correction for concentrated electrolyte systems.

Findings

Reveals ion speciation transitions with concentration and temperature.

Predicts solubility and phase behavior consistent with experiments.

Provides insights into interfacial nucleation in precipitation.

Abstract

Understanding concentrated electrolytes requires a theory that spans local hydration and mesoscale interfacial assembly. We present an integrated workflow-SCOPE-that combines (i) enhanced sampling focused on a single Li+ ion, (ii) reweighting of biased trajectories to recover equilibrium microstate probabilities, and (iii) a chemical-potential correction that accounts for the limited reservoir of free water in finite simulation boxes. Applied to LiCl(aq) across 0.5-26 M and 283-313 K, this approach reveals a simple organizing principle: solvated ions dominate at low concentration; contact ion pairs emerge at intermediate strength; and aggregated Li-xCl clusters become most stable at the solubility limit. The resulting free-energy trends predict temperature-dependent solubility in close agreement with experiment and clarify the role of interfacial nucleation in precipitation. Beyond the simple LiCl(aq) salt considered here, SCOPE offers a transferable strategy for characterizing speciation and phase behavior in concentrated liquid systems where collective coordinates and rare events dominate.