Practical considerations for finite concentration molecular dynamics simulations

Understanding concentrated electrolytes requires a theory that spans local hydration and mesoscale interfacial assembly. We present an integrated workflow-Solvation Characterization via Optimized Probability Ensemble averaging (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 0.5-26M and 283-313 K, this approach reveals a simple organizing principle: solvated ions dominate at low concentrations; contact ion pairs emerge at intermediate strengths; 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.