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Impact of three-body interactions in a ReaxFF force field for Ni and Cr transition metals and their alloys (corrected proof PDF)

Corpus PDF role

Corrected proof PDF (Shin_CompMatSci_NiCr_metal_2021_galley.pdf). The journal PDF is Shin_CompMatSci_NiCr_metal_2021.pdf on 2021shin-computationa-impact-three-body.

Summary

fcc nickel elasticity and defect energetics are sensitive to angular restoring forces that two-body-centric ReaxFF metal descriptions can mishandle: in particular, C\(_{12}\) and C\(_{44}\) can collapse to equality, and stacking-fault energies can become negative, spuriously accelerating fcc→hcp transformations. This work augments Ni and Cr ReaxFF parameterizations with explicit three-body (valence-angle) terms, then benchmarks thermal and mechanical responses against DFT and experiment. Finite-temperature elastic constants for fcc Ni and bcc Cr, thermal expansion from 0 to 1700 K, melting temperatures via hysteresis MD with large cells and voids, and Ni–Cr alloy formation energetics (Ni\(_3\)Cr ordering vs bcc solid solutions) are reported. The overarching claim is that three-body physics is necessary for semiquantitative metal property prediction within the ReaxFF framework for these systems.

Abstract-level motivation stresses that prior Ni/Cr ReaxFF metals omitted explicit angular terms, producing unphysical elastic degeneracies and unstable stacking faults that bias phase transformation kinetics; adding optimized valence-angle interactions is presented as restoring cubic elastic structure and sensible fault energies before finite-temperature melting and alloy tests.

Readers should verify numerical values, units, and section references against the peer-reviewed PDF and any Supporting Information, especially when extracts or galley PDFs truncate tables.

Methods

Authoritative protocol: Use [[2021shin-computationa-impact-three-body]] (journal PDF) for tables, timestep, and thermostat settings; this slug documents only the corrected-proof PDF path.

A — ReaxFF (Ni / Cr / Ni–Cr)

B — MD benchmarks

  • Elastic, thermal expansion, melting (hysteresis with voids) as summarized on the VOR page.

C — DFT

  • Reference alloy formation energies and 0 K elastic data for comparison to ReaxFF.

D — Experiments

  • Literature elastic and melting benchmarks as cited on the VOR page.

1 — MD application (atomistic dynamics)

  • Engine / code: LAMMPS (or the MD package named in the publication) runs reactive/classical molecular dynamics as described in the peer-reviewed PDF (version/build details in the article).
  • System size & composition: Supercell / slab models with explicit atom counts and overall composition are specified in the primary text (numeric tables may live only in the PDF/SI).
  • Boundaries / periodicity: PBC (periodic boundary conditions) are used for bulk/liquid–surface cells unless the authors document non-periodic directions or frozen regions.
  • Ensemble: NVT (canonical) trajectories are reported unless the PDF instead emphasizes NPT segments for stress/volume control.
  • Timestep: timestep settings in fs (femtosecond units) appear in the Methods/LAMMPS discussion in the PDF.
  • Duration / stages: Equilibration plus production runs spanning ps–ns cumulative sampling are described in the article.
  • Thermostat: Nose–Hoover, Berendsen, Langevin, or related thermostat choices (damping/time constants) are given in the publication’s MD protocol.
  • Barostat: N/A — pressure coupling is not invoked for strictly constant-volume NVT cells summarized here; see the PDF for any NPT Parrinello–Rahman/barostat usage.
  • Temperature: temperature programs and set-points (K) are stated in the simulation protocol.
  • Pressure: N/A — pressure is not an independent control variable under the NVT summaries in this note; consult NPT sections in the PDF if applicable.
  • Electric field: N/A — electric field / static bias coupling is not highlighted for production MD in this wiki summary (defer to PDF if bias appears).
  • Replica / enhanced sampling: N/A — umbrella sampling, metadynamics, replica exchange, or other enhanced sampling / rare event workflows are not noted in this summary unless the PDF states otherwise.

2 — Force-field training (when applicable)

  • Parent FF / elements: parent ReaxFF (or other reactive) force field / parameter set names and element coverage follow the tables in the PDF.
  • QM reference: DFT/QM reference calculations (functional, basis set, k-point or cutoff conventions) underpin the training data described in the article.
  • Training set: Training geometries, reaction subsets, equation of state targets, or other reference data sets are enumerated in the fitting section of the PDF.
  • Optimization: optimization / least-squares or packaged (CMA-ES, genetic algorithm, etc.) parameter fit procedures appear in the Methods as implemented by the authors.
  • Reference data: additional experimental or literature DFT benchmark sets cited for validation are listed in the publication.

Findings

Three-body terms remove the C\(_{12}\)=C\(_{44}\) degeneracy and improve stacking-fault energetics for fcc Ni relative to the prior two-body-limited description. Melting temperatures land near 1698 K for Ni (~1.7% of experiment) and 2410 K for Cr (~10%), with hysteresis sensitivity discussed in the text. Ni\(_3\)Cr heat of formation is negative (favoring order) while bcc solid-solution motifs show positive heats in the tests shown, consistent with DFT trends. Elastic constants at 0 K match DFT within roughly 5–10% except where the abstract flags a larger deviation in C\(_{33}\).

Comparisons (corpus). Cite the VOR [[2021shin-computationa-impact-three-body]] for final typeset figures and any table-level agreement with experiment; this proof path is for ingest provenance only.

Limitations

Remaining elastic discrepancies (notably C\(_{33}\)) and melting hysteresis dependence on simulation setup are acknowledged in the paper. Proof pagination may differ from the VOR PDF on 2021shin-computationa-impact-three-body.

Reader notes (navigation)