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Atomistic insight into the effects of electrostatic fields on hydrocarbon reaction kinetics

Summary

Reactive MD (ReaxFF CHO-2016 hydrocarbon combustion field) and DFT are cross-compared to assess field-induced polarization and the coupling of external electrostatic fields to reaction pathways and transport in hydrocarbon oxidation / pyrolysis contexts, culminating in large-scale n-dodecane + O₂ combustion simulations with imposed electric fields. The work targets settings such as plasma-assisted or field-enhanced combustion where explicit electrostatic coupling may not be negligible relative to thermal driving forces.

The J. Chem. Phys. abstract motivates the study by noting that electric fields can alter reaction rates even when thermal effects are modest, and that atomistic models must self-consistently treat charge redistribution, collisional energy transfer, and field–dipole alignment for polar versus nonpolar species in oxidizing environments.

Methods

Charge response validation (A/C)

Compare ReaxFF QEq under E-fields to DFT charge partitioning schemes for molecular/cluster polarization (partitioning choices in the article).

Barrier shifts (C)

NEB-type paths for selected steps under oriented fields to quantify oxidation vs pyrolysis-class barrier changes.

Molecular collision tests (B)

ReaxFF bimolecular trajectories separating Lorentz vs Coulomb contributions vs orientation/polarity.

Large-scale combustion MD (B)

n-Dodecane/O\(_2\) with strong E-fields; monitor translational/rotational vs vibrational energy channels.

Validation ladder

Small-system charge/barrier checks before macroscale reactive cells to avoid thermal masking of field effects.

1 — MD application (atomistic dynamics)

Engine / code: LAMMPS with the ReaxFF CHO-2016 hydrocarbon combustion field. Systems & composition: subsections span QEq/charge benchmarks, bimolecular collision cells, and large-scale n-dodecane + O\(_2\) combustion with imposed static external electric fields (magnitude, orientation, and duration are in the JCP article, not re-tabulated here). Boundaries / periodicity: PBC for gas-phase combustion MD as implemented in the paper. Ensemble, timestep, production length, thermostat, barostat: the large n-dodecane/O\(_2\) combustion MD and the cluster tests are run with LAMMPS-standard NVT/NVE-like choices (per scenario) over ps–ns spans as tabulated; N/A for re-listing every NVT thermostat and ns duration in this wiki (see JCP). Temperature / pressure / stress: set by the scenario in each section (e.g. combustion vs cluster tests); N/A for a single table on this page. Electric field: central to the work—oriented fields in MEP/NEB analyses, Lorentz-related effects in bimolecular tests, and field-coupled macroscale reacting flows. Coulomb / QEq update: ReaxFF charge equilibration compared to DFT partitioning. Shear, shock: N/A in the abstracted scope. Enhanced-sampling MD: N/A — the pathway tool is NEB (minimization/path search), not umbrella metadynamics in MD.

2 — Force-field training

N/A — the study uses a published ReaxFF CHO line; training new parameters is not the focus.

3 — Static QM (DFT)

DFT supplies reference charges and supports MEP/NEB barriers under fields for oxidation vs pyrolysis classes. N/A — program, functional/basis/k-sampling, and all numerical settings appear in the JCP main text and SI, not in this short wiki page.

Findings

QEq vs DFT

Field-induced charges from ReaxFF track DFT trends sufficiently (per abstract) to justify large reactive runs.

Pathway selectivity

MEP results suggest fields can accelerate/inhibit oxidation more than pyrolysis steps in their C/H electronegativity argument.

Species polarity

Polar molecules align and show kinetic changes; apolar species respond mainly through weak induced dipoles.

Combustion-scale observations

Strong fields couple translation/rotation to charge transfer and can reduce vibrational excitation via stabilization-type effects in their analysis.

Design knob

Field alignment with dipoles can bias rotational vs vibrational heating by species polarity.

The abstract-level takeaway repeated in the JCP entry is that electrostatic biases can be nonthermal levers on reaction selectivity when polarization and collisional energy partitioning are treated together—motivating the validation ladder (small cluster tests before large combustion cells) described above.

Limitations

Field strengths and system sizes may not map directly to laboratory flames; ReaxFF chemistry uncertainties remain for combustion under extreme conditions.

Relevance to group

van Duin-authored electrostatic-field–coupled ReaxFF combustion study with Lele; complements other field-coupled reactive MD threads in the corpus.

Citations and evidence anchors