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eReaxFF: A pseudoclassical treatment of explicit electrons within reactive force field simulations

Summary

Same J. Chem. Theory Comput. article as [[2016islam-venue-ct6b00432]] (DOI 10.1021/acs.jctc.6b00432): eReaxFF augments ReaxFF with pseudoclassical explicit electrons, integrates ACKS2 charging, trains on electron affinities, and benchmarks MD against Ehrenfest dynamics for hydrocarbon radicals. The abstract claims large speedups over quantum chemistry dynamics while keeping most literature ReaxFF parameters fixed during the explicit-electron extension.

Methods

Same article as 2016islam-venue-ct6b00432 (DOI 10.1021/acs.jctc.6b00432). This slug’s pdf_path is an ACS proof export (papers/Islam_JCTC_eReaxFF_2016_proof.pdf); pagination may differ from the version-of-record PDF on 2016islam-venue-ct6b00432.

MD application. Section IV.A uses molecular dynamics in NVT relaxation at 1 K, then NVT production at 400, 500, and 600 K with a Berendsen thermostat (100 fs damping), 0.1 fs timestep, and velocity Verlet on C₁₂H₁₉• and C₁₄H₂₃• hydrocarbon radicals (stoichiometry per formulas) with explicit excess electrons, compared to Ehrenfest references. Boundary conditions are gas-phase isolated radical models without NPT barostats or applied electric driving; segment lengths follow Figures 3–4 and Section IV.A (multi‑ps evolution).

Force-field training. eReaxFF augments ReaxFF with explicit Gaussian electrons and ACKS2 charging (Section II). A successive one-parameter search fits electron affinities across bonding classes while freezing most literature ReaxFF parameters. M06-2X/aug-cc-pVTZ in Jaguar 7.5 provides spot checks where eReaxFF and experiment disagree (Section III).

Standalone static QM study. N/A — DFT supports EA training and validation only.

Findings

eReaxFF reproduces qualitative EA trends versus experiment for the training set while standard ReaxFF fails many of the same targets (Figure 2). MD captures electron transfer along the conjugated–aliphatic–radical pathway for C₁₂H₁₉• at 400–600 K, with faster hopping at higher temperature (Section IV.A). Benchmarks include experiment, Ehrenfest dynamics, and DFT spot checks. The authors note that quantum calculations delocalize the added electron more than the pseudoclassical carriers and position eReaxFF as a scalable alternative to expensive time-dependent DFT dynamics.

Corpus honesty. Prefer 2016islam-venue-ct6b00432 for version-of-record pagination.

Limitations

Corpus file is an ACS proof PDF; cite JCTC version-of-record for final pagination. - Pseudoclassical electrons are not full TD-DFT; accuracy is method-dependent. - Explicit-carrier dynamics should be validated on a case-by-case basis when migrating parameters between chemistries, because redox environments can stress pieces of the ACKS2 coupling that were not included in the training targets highlighted in the abstract.

Relevance to group

Foundational eReaxFF methods paper from the van Duin collaboration—prerequisite reference for 2016islam-venue-jp6b08688 and later battery interface studies.

Citations and evidence anchors

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