Development of a ReaxFF Force Field for Cu/S/C/H and Reactive MD Simulations of Methyl Thiolate Decomposition on Cu (100)

It has been shown that the rate of
decomposition of methyl thiolate
species on copper is accelerated by sliding on a methyl thiolate covered
surface in ultrahigh vacuum at room temperature. The reaction produces
small gas-phase hydrocarbons and deposits sulfur on the surface. Here,
a new ReaxFF potential was developed to enable investigation of the
molecular processes that induce this mechanochemical reaction by using
density functional theory calculations to tune force field parameters
for the model system. Various processes, including volumetric expansion/compression
of CuS, CuS2, and Cu2S unit cells; bond dissociation
of Cu–S and valence angle bending of Cu–S–C;
the binding energies of SCH3, CH3, and S atoms
on a Cu surface; and energy for the decomposition of methyl thiolate
molecular species on copper, were used to identify the new ReaxFF
parameters. Molecular dynamics simulations of the reactions of adsorbed
methyl thiolate species at various temperatures were performed to
demonstrate the validity of the new potential and to study the thermal
reaction pathways. It was found that reaction is initiated by C–S
bond scission, consistent with experiments, and that the resulting
methyl species diffuse on the surface and combine to desorb ethane,
also as found experimentally.