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Influence of metal ion intercalation on the vibrational dynamics of water confined between MXene layers

Abstract

INS on pristine and Li/Na/K-intercalated Ti₃C₂Tₓ with ReaxFF MD (ADF) on interlayer water: larger ions correlate with more ordered, slower water in experiment and simulation.

Summary

This slug is a publisher proof PDF (Osti_PhysicsMat_2017_proof.pdf) for the same Phys. Rev. Mater. article curated under 2017osti-venue-paper (papers/Osti_PhysicsMat_2017.pdf). After the cover letter, the proof contains the full paper on inelastic neutron scattering of water in Ti₃C₂Tₓ with Li⁺/Na⁺/K⁺ intercalation, paired with ReaxFF molecular dynamics (implementation in ADF, ReaxFF citations [27,28] in the article text). The MD section describes ~1776-atom supercells with two MXene layers, energy minimization (200 steps), NPT equilibration at 300 K (20 ps) with fixed in-plane lattice parameters, then NVT thermalization and 200 ps production NVT with weak thermostat coupling for sampling. INS shows much stronger hydrogen signal for pristine vs ion-intercalated samples; intercalation removes substantial interlayer water and changes GVDS of vibrations. MD reproduces increased ordering and reduced mobility with larger intercalated cations.

Methods

This slug tracks the APS publisher proof PDF (papers/Osti_PhysicsMat_2017_proof.pdf); the scientific content matches 2017osti-venue-paper (Phys. Rev. Mater. 1, 065406; DOI 10.1103/PhysRevMaterials.1.065406). The in-repo proof extract normalized/extracts/2017osti-venue-paper-2_p1-2.txt is cover-letter pages only, so protocol details below follow the article body bundled in the proof PDF (same Methods as the VOR) rather than that extract.

1 — MD application (atomistic dynamics)

  • Engine / code: ReaxFF molecular dynamics carried out with ADF (ADF2016) as stated in the article body on this proof; export pages precede the formatted article in this file.
  • System size & composition: Supercells of order ~1776 atoms containing two Ti\(_3\)C\(_2\)T\(_x\) layers with intercalated Li\(^+\)/Na\(^+\)/K\(^+\) and confined water in the arrangement used for INS comparison.
  • Boundaries / periodicity: Three-dimensional periodic supercells (standard for slab gallery models in the article; confirm facet vectors in the formatted pages).
  • Ensemble: NPT equilibration segment followed by NVT production sampling as described in the article body summarized on the sibling VOR note.
  • Timestep: N/A here — explicit fs value is not on the cover-letter extract; read the formatted Methods in the proof PDF or 2017osti-venue-paper’s pdf_path.
  • Duration / stages: Energy minimization (200 steps reported in the article body on this proof), NPT equilibration at 300 K for ~20 ps with fixed in-plane lattice parameters, then ~200 ps NVT production with weak-coupling temperature control (values as tabulated in the article).
  • Thermostat: Weak-coupling temperature control during NVT production as described in the article body on this proof (exact algorithm label on the formatted Methods pages).
  • Barostat: NPT segment uses anisotropic volume control consistent with fixed in-plane lattice constants as described in the article; confirm barostat label in the formatted Methods.
  • Temperature: 300 K for the MD equilibration/production windows quoted above.
  • Pressure: N/A for the NVT production segment; NPT segment controls stress tensor components as described in the article.
  • Electric field: N/A — not applied in the MD protocol summarized for the INS comparison.
  • Replica / enhanced sampling: N/A — conventional MD stages only.

2 — Force-field training

N/A as a new fit — the publication employs a published ReaxFF parametrization for MXene–water–ion interactions (cited training literature in the article).

3 — Static QM / DFT-only

N/A — INS is the primary experimental observable; QM is not the production spectroscopy engine.

4 — INS experiment (mirrors VOR page)

SEQUOIA measurements with E\(_i\) = 50, 160, 250, 600 meV and VISION baselines for water / 2 M hydroxide solutions; HF-derived Ti\(_3\)C\(_2\)T\(_x\) processed with 2 M LiOH/NaOH/KOH intercalation, XRD, and 110 °C (4 h) vacuum drying, plus the 150 °C hydrogen-removal step for pristine material (Sec. II.A text shared with 2017osti-venue-paper).

Findings

Outcomes and mechanisms

INS shows interlayer water with bulk-like disorder for pristine Ti\(_3\)C\(_2\)T\(_x\), but much less confined water and more ordered hydrogen-bond environments after alkali intercalation, with ordering that increases with cation size in the article’s analysis.

Comparisons

ReaxFF MD reproduces the trend of reduced mobility and stronger spatial interference among water molecules as intercalated alkali size grows, consistent with the INS-derived picture and with earlier quasielastic discussion of K\(^+\)-intercalated MXenes.

Sensitivity / design levers

Ion identity (Li vs Na vs K) and post-synthesis drying/anneal history strongly modulate how much water remains in the gallery—both must stay consistent between INS specimens and simulation cells.

Limitations, outlook, and corpus honesty

Prefer 2017osti-venue-paper for automation keyed to the VOR blob hash; this proof PDF adds workflow/cover pages that can shift pagination. Operators should cite DOI + journal pagination from the formatted article, not the proof letterhead, when archiving simulation metadata. Full spectral interpretation and any author-stated caveats belong to the formatted Phys. Rev. Mater. text inside this PDF bundle.

Limitations

Proof PDF adds workflow pages; prefer 2017osti-venue-paper for stable file naming in automation. INS instrument resolution and multiple incident energy settings influence how G(E) features map onto MD spectral comparisons; use the article’s figure captions when aligning simulation timestep and sampling windows to neutron data. Keep hydration history and intercalation routes synchronized between experiment and simulation when comparing ion-size trends.

Relevance to group

Adri C. T. van Duin and Alireza Ostadhossein co-authorship; neutron + ReaxFF pairing for MXene electrolyte confinement.

Citations and evidence anchors

  • DOI: 10.1103/PhysRevMaterials.1.065406

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