Development and validation of a ReaxFF reactive force field for the pyrolysis of fluorine-containing gas systems.

CONTEXT: Existing fluorine-containing ReaxFF parameterizations have primarily been developed for high-energy materials, HF-silica etching, fluorinated polymers, or polymer-metal interfaces, and their training and validation domains do not specifically cover the coupled gas-phase chemistry of perfluoroketone pyrolysis, including fluorinated carbonyl environments, competing C-C and C-F bond scission, fluorinated radical intermediates, and H·-mediated HF formation. To address this application-specific gap, the present work develops a C-H-O-F ReaxFF parameterization tailored to the gas-phase pyrolysis chemistry of perfluorohexanone and related fluorinated fire-extinguishing agents. The resulting force field is evaluated against a multilevel DFT reference database spanning equilibrium structures, bond and angle distortions, and representative HF-related reaction profiles, followed by an application-oriented assessment in large-scale reactive MD simulations.

METHODS: All DFT reference data for force field training were obtained at the M06-2X/6-311 +  + G(d,p) level. The ReaxFF parameters were optimized through a sequential single-parameter search with a weighted error objective function. The force field was benchmarked through comparisons of bond dissociation curves, angle-bending potential-energy profiles, and representative reaction-energy profiles against DFT calculations. An application-oriented assessment using 1000 perfluorohexanone molecules and 1000 H· radicals at 1400-3000 K showed increasing parent-molecule conversion with increasing temperature under the investigated accelerated simulation conditions.