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Oxidation of nickel surfaces through the energetic impacts of oxygen molecules: Reactive molecular dynamics simulations

Summary

Reactive molecular dynamics with ReaxFF studies hyperthermal oxidation of Ni(100) and Ni(111) by 5 eV O₂ impacts at surface temperatures of 300, 600, and 900 K. The work connects impact-driven nucleation, growth kinetics (island versus Langmuir-like descriptions), oxygen uptake versus temperature, and the amorphous structure of the growing NiO film, with analysis of radial distribution functions, oxygen density profiles, and charge distributions. The J. Chem. Phys. article targets aerospace-relevant hyperthermal atomic/molecular oxygen scenarios where impact energy deposits locally and drives non-equilibrium oxide nucleation.

Methods

MD application (atomistic dynamics)

  • Engine / code: LAMMPS (parallel ReaxFF integration path cited in the Computational Details section) with variable-charge ReaxFF for Ni–O chemistry.
  • Force-field lineage: Ni–O parameters are taken from the Zou et al. ReaxFF training line referenced in the article (with additional Ni/O oxide formation benchmarks discussed there against QM heats of formation).
  • Surfaces / supercells: Ni(100) in a (9×9) surface unit cell (162 surface Ni atoms) and Ni(111) in a (7×7) cell (196 surface Ni atoms), each with eight Ni layers in Z (Table I in the article).
  • Boundaries / periodicity: Periodic in XY during equilibration and the hyperthermal impact stage; Z is treated as the non-periodic direction for gas-phase O₂ approach (normal incidence), consistent with the slab-with-vacuum geometry described in Computational Details.
  • Equilibration: Substrates coupled to a Berendsen thermostat for 20 ps at 300, 600, or 900 K (damping 0.1 ps), then 10 ps NVE relaxation before impacts.
  • Impact protocol: O₂ molecules introduced every 2.5 ps at 15 Å above the surface, 5 eV translational energy, normal incidence, random XY placement; Berendsen thermostat used to remove excess energy before each new impact as described in the article.
  • Ensemble during oxidation: The protocol uses Berendsen thermalization during substrate equilibration, a short NVE segment (10 ps) after equilibration, then hyperthermal O₂ impacts with Berendsen cooling before each new impact to remove excess energy (Computational Details in J. Chem. Phys. 144, 144705).
  • Timestep: 0.25 fs (velocity Verlet integration stated in Computational Details).
  • Duration / sampling: Results quoted in the abstract follow 200 successive O₂ impacts per supercell for growth-rate and film-structure analysis.
  • Thermostat: Berendsen during substrate equilibration (20 ps, damping 0.1 ps) and between successive O₂ impacts; N/A — Nosé–Hoover is not the thermostat used in the documented hyperthermal oxidation loop.
  • Barostat: N/A — not used in the documented hyperthermal oxidation workflow.
  • Temperature: Substrate setpoints 300 / 600 / 900 K for the compared series.
  • Pressure: N/A — not a controlled thermodynamic variable in the impact protocol described.
  • Electric field: N/A — not used.
  • Replica / enhanced sampling: N/A — not used.
  • Diagnostics: Oxygen uptake vs impact count, RDFs, oxygen density profiles, and charge profiles across Ni | NiO for film morphology.

Force-field training

N/A — application paper using a literature ReaxFF Ni/O parameterization with QM benchmarks cited for validation; it does not report a new ReaxFF optimization campaign as the contribution.

Static QM / DFT

N/A — not a DFT production study; QM values appear as reference heats of formation for force-field context in the ReaxFF section, not as AIMD results driving the oxidation trajectories.

Findings

  • Nucleation sites: Under 5 eV O₂ impacts, primary oxide nuclei can appear at arbitrary impact sites, contrasting with island-perimeter-limited pictures from some thermal oxidation scenarios discussed in the introduction.
  • Growth law comparison: The authors report that an island-growth picture does not accurately describe their simulated uptake kinetics; under these hyperthermal conditions growth is described as closer to a Langmuir-type law.
  • Temperature sensitivity: Raising the surface temperature from 300 K to 900 K increases oxygen consumption by about 18.75% on Ni(100) and about 23% on Ni(111) by the end of the 200-impact series (abstract values).
  • Film structure: After 200 impacts, the NiO film is amorphous according to RDF and density-profile diagnostics in the article.
  • Plasticity / twins: Additional mechanical-response discussion (including twinning) appears later in the full text beyond the abstract-level oxidation summary—consult pdf_path for stress–strain context if linking this paper to nanomechanics notes.

Limitations

Another corpus slug (2016amiri-venue-oxidation-nickel-2) points to a second PDF with the same DOI—verify checksum when deduplicating.

Wiki prose here is a navigation aid. Definitive numbers, protocol details, and figure-level claims should be taken from the peer-reviewed article at pdf_path (and any Supporting Information cited there), not from this page alone.

Relevance to group

Reactive MD/ReaxFF lineage for metal oxidation under energetic oxygen exposure (aerospace-relevant hyperthermal conditions).

Citations and evidence anchors