Skip to content

Development of a ReaxFF force field for Cu/S/C/H and reactive MD simulations of methyl thiolate decomposition on Cu(100)

Evidence and attribution

Authority of statements

Prose sections below (Summary, Methods, Findings, etc.) are curated summaries of the publication identified by doi, title, and pdf_path in the front matter above. They are not new primary claims by this wiki.

For definitive numerical values, reaction schemes, and interpretations, use the peer-reviewed article (and optional records under normalized/papers/ when present)—not this page alone.

Summary

This Journal of Physical Chemistry B article develops a new ReaxFF parameterization for Cu/S/C/H chemistry to study methyl thiolate decomposition on Cu(100). The scientific motivation comes from surface-science experiments in which sliding on a methyl thiolate-covered copper surface in ultrahigh vacuum at room temperature accelerates decomposition, producing small gas-phase hydrocarbons and leaving sulfur on the surface, a process argued to be mechanochemical rather than thermally dominated under the stated mild sliding conditions. To enable atomistic simulation of these pathways, the authors fit ReaxFF parameters using density functional theory data for bulk copper sulfide phases, bond dissociation and angle bending involving Cu–S–C motifs, binding energies of SCH\(_3\), CH\(_3\), and S on copper, and potential energy curves for methyl thiolate decomposition on Cu(100). The collaboration spans UC Merced, UW–Milwaukee, Penn State (van Duin), and surface-science and tribology expertise (Tysoe; Martini).

Methods

A — Force-field training / fitting: ReaxFF parameters optimized against DFT for Cu/S/C/H: EOS of CuS, CuS\(_2\), Cu\(_2\)S; Cu–S dissociation; Cu–S–C angles; adsorption of SCH\(_3\), CH\(_3\), S; methyl thiolate decomposition paths on Cu(100). Software: standalone ReaxFF fitter + LAMMPS for validation MD (per article/SI).

B — Molecular dynamics / sampling: Reactive MD of adsorbed methyl thiolate on Cu(100) at elevated T to compare pathways/products with UHV experiments. Rare-event/Bell-type mechanochemical context in text—numerical timestep, ensemble, duration in SI.

C — DFT / static QM: Training QM for bulk sulfides, surfaces, and reaction PES slices—functional/basis per Methods (see paper).

D — Review / non-simulation framing: Primary JPCB parameterization + application—not a literature review.

Engine: LAMMPS ReaxFF validation MD for methyl thiolate on Cu(100). System: Cu(100) slab with adsorbed CH\(_3\)S– / decomposition products; atom counts and supercell repeats are in article/SI. Ensemble: NVT for the elevated-temperature reactive MD validation trajectories (confirm NVE segments, if any, in SI). Timestep / thermostat / duration / PBC / barostat: N/A — numerical inputs are not duplicated on this wiki page—copy from pdf_path. Temperature: elevated T (exact setpoints in SI). Pressure: N/A — UHV-style chemistry is discussed experimentally, but MD barostat targets are not summarized here. Electric field: N/A — not used in the summarized MD (mechanochemistry is contextual). Replica / enhanced sampling: N/A — not used.

Findings

The reactive simulations identify C–S bond scission as the initiation step for methyl thiolate decomposition, consistent with the experimental picture emphasized in the abstract. After scission, methyl species diffuse on the surface and combine to desorb ethane, again matching experimental observations summarized in the article. The work is presented as a demonstration that the newly fitted ReaxFF potential can capture the methyl thiolate decomposition chemistry on Cu(100) sufficiently well to support further studies of mechanochemistry at copper–organosulfur interfaces.

The introduction further contrasts thermally driven extreme-pressure lubricant chemistry at very high interfacial temperatures with mild sliding conditions where tribofilm formation can be mechanochemically accelerated without appreciable temperature rise, using dialkyl disulfide chemistry on copper in ultrahigh vacuum as the experimental anchor for the methyl thiolate family. That framing motivates reactive MD not only as a barrier-fitting exercise but as a route toward molecular interpretations of parameters such as activation length in stress-biased rate models, while acknowledging oversimplifications of collinear force assumptions.

Limitations

  • Scope centers on Cu(100) methyl thiolate family chemistry; broader additive chemistry requires further validation.

Relevance to group

Shows van Duin ReaxFF deployment for organosulfur Cu interfaces linking surface science and tribochemistry.

Citations and evidence anchors

  • DOI: 10.1021/acs.jpcb.7b06976 (papers/Yeon_CuSCH_JPCB_2017.pdf).
  • Text-aligned pointers: normalized/extracts/2017jejoon-yeon-j-phys-chem-development-reaxff_p1-2.txt

Reader notes (navigation)