Development of a ReaxFF reactive force field for Pt/Cl systems with application to platinum metal etching with chlorine and hydrogen chloride gases
Corpus note
The repository holds a galley PDF; cite the version of record using the DOI.
Summary¶
Platinum surfaces in catalysis, electrochemistry, and microfabrication routinely encounter chlorine and hydrogen chloride during plasma etching, chlorination, or wet processing steps that reshape nanoscale features. Talkhoncheh et al. develop a ReaxFF parametrization for Pt/Cl/H chemistry so reactive molecular dynamics can follow chlorine adsorption, dissociation, surface chloride formation, and evolution of volatile Pt\(_x\)Cl\(_y\) species without on-the-fly quantum chemistry. Training uses DFT-quality adsorption and reaction energies on Pt(100) and Pt(111), equation-of-state data for PtCl\(_2\) crystal phases, and chlorine diffusion barriers on platinum facets, followed by validation against gas-phase Cl\(_2\) and HCl exposure simulations compared to measured etch-rate ratios that bench-mark industrial halogen etch chemistries.
Methods¶
ReaxFF training (A)¶
Standard bond-order fit; DFT database on Pt(100)/(111) adsorption/reactions, PtCl\(_2\) EOS, Cl diffusion—see J. Phys. Chem. A 10.1021/acs.jpca.4c01708 and papers/Talkhoncheh_JPCA_PtCl_etching_galley.pdf.
Reactive MD etching benchmarks (B)¶
LAMMPS Pt(100)/(111) slabs + Cl\(_2\)/HCl at T/P tied to experiment; track volatile Pt\(_x\)Cl\(_y\) and surface chlorides for facet anisotropy and rate-ratio validation.
Training-data categories (summary). The DFT database includes Cl and HCl adsorption motifs on Pt(100) and Pt(111), PtCl\(_2\) crystal equations of state, and Cl diffusion pathways relevant to subsurface penetration versus surface chlorination. Optimization targets weighted adsorption energies, reaction barriers, and bulk phase stabilities so that ReaxFF reproduces the QM ordering needed for facet-dependent etch fronts.
MD application (reactive etching validation). Pt(100)/(111) slab models in LAMMPS+ReaxFF are exposed to Cl\(_2\) and HCl at temperature/pressure conditions in the published Methods (e.g. room-temperature-scale and elevated K setpoints; N/A—copy exact K and bar from the J. Phys. Chem. A file). Periodic PBC slab supercells; NVT is used in the production-style runs summarized here (N/A—barostat not used in constant-volume gas–surface etching in the cited NPT-free protocol). N/A—exact time step (fs), run lengths (ps/ns), and Nosé–Hoover/Berendsen thermostat parameters: copy from the version-of-record text. N/A—no static external electric field; N/A—umbrella or replica sampling not part of the validation workflow. System size in atoms and thickness of passivated layers, if any, are in the article.
Findings¶
Pt(100) chlorinates and loses platinum faster than Pt(111) under comparable exposure because the more open terrace presents additional reactive sites and faster pathways to volatile chlorides. Pt(111) remains comparatively passivated: subsurface chlorine penetration is slower, delaying deep etch fronts. Simulated HCl versus Cl\(_2\) etch-rate ratios agree satisfactorily with experiment, supporting the ReaxFF workflow as an atomistic interpretation aid for platinum halogen chemistry. The fitted database explicitly spans Cl adsorption, HCl dissociation, PtCl\(_2\) bulk behavior, and facet-dependent chlorine diffusion, jointly controlling whether etching stays surface-limited or invades the bulk metal.
These mechanistic differentiators matter for interpreting facet-dependent roughening and particle formation in halogen-based platinum etch recipes used across catalysis toolchains and microfabrication lines. Industrial users should still map simulation exposure conditions to tool pressure, flow, and plasma radical fluxes tabulated in the article.
Limitations¶
The repository PDF is a galley; pagination may differ from the journal issue. Copy numerical pressures, dosages, and averaging windows from the published article rather than this summary, and prefer the version-of-record PDF for bibliographic page locators.
Relevance to group¶
Illustrates ReaxFF training for noble-metal halide chemistry with industrial etching validation—adjacent to broader surface reaction parameterization efforts.
Citations and evidence anchors¶
- DOI:
10.1021/acs.jpca.4c01708