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ReaxFF molecular dynamics simulations of electrolyte–water systems at supercritical temperature

Corpus note

A galley/author-proof sibling is 2020dasgupta-venue-total-number; prefer the version-of-record PDF for pagination when both are present. See docs/corpus/NON_PRIMARY_ARTICLE_PAPER_SLUGS.md for non-primary PDF roles.

ReaxFF MD of alkali chloride pairs in water at 700 K spans multiple densities to map RDFs/ADFs, ion diffusion, H-bond residence times, Voronoi voids, and ion clustering under supercritical conditions.

Summary

Supercritical aqueous electrolytes exhibit void-rich morphologies and altered dielectric screening that change ion pairing and transport. The paper reports ReaxFF trajectories for LiCl, NaCl, KCl, RbCl, CsCl in periodic cells with water density swept from liquid-like to vapor-like at 700 K, mapping how void topology and ion clustering track M⁺ identity and ρ. Coordination stats, angular distributions, H-bond residence times, and self-diffusion are reported relative to that grid; consult the J. Chem. Phys. article and any SI for authoritative tables.

Methods

  • Engine / integrator: ReaxFF molecular dynamics with velocity Verlet integration in the J. Chem. Phys. implementation (see article for code details).
  • System size & composition: Alkali chloride + water periodic cells with atom counts and box edge lengths per salt and ρ in Table I (each state point at 700 K).
  • Potential: ReaxFF parameterization for water and alkali/halide interactions as cited in the article (prior ReaxFF water/electrolyte references).
  • Integrator: Velocity Verlet with timestep 0.25 fs (as stated).
  • Thermostat: Berendsen thermostat with 100 fs temperature damping applied to the entire system (per Methods text).
  • State points: 700 K with tabulated simulation box sizes for each salt at water densities ρ = 1.00, 0.70, 0.35, and 0.15 g cm\(^{-3}\) (Table I in the paper).
  • Duration / production: N/A for a single unified ns line in the Methods abstract on this page—equilibration and analysis windows are given in the JCP text and should be read there.
  • Analysis: RDF/ADF, mean-square displacement for diffusion, residence-time distributions for water around ions, Voronoi polyhedra void analysis, clustering statistics for salt aggregates.
  • PBC 3D periodic electrolyte boxes at each (salt, \(\rho\), 700 K) state point. NVT-style thermostatting via Berendsen (see above); N/A — barostat and NPT control (constant pressure) are not the focus of the stated sampling—isochoric ρ grids at fixed T. N/A — hydrostatic pressure servo in production if density is fixed per Table I. Electric field: N/A; replica/umbrella: N/A.

Findings

  • Coordination of water around cations rises with ionic radius along the alkali series at the studied conditions.
  • Self-diffusion of cations increases as density decreases, linked to larger void volumes in the fluid.
  • Li\(^+\) shows the longest water residence (highest “retaining” tendency) among ions compared in the residence-time analysis.
  • At low density, Na\(^+\) and K\(^+\) can form salt clusters as dielectric screening weakens; voids and ion nucleation dramatically alter transport relative to dense liquid-like states.
  • Sensitivity is primarily to ρ and M\(^+\) identity at fixed 700 K in the sweep described.

Limitations

700 K and reduced densities accelerate chemistry and vapor-like behavior beyond ambient battery electrolytes; quantitative agreement with experiment requires careful potential validation.

Relevance to group

van Duin-group ReaxFF on supercritical water + electrolytes, relevant to hydrothermal and extreme-environment aqueous chemistry.

Citations and evidence anchors