Identifying Collisions of Various Molecularities in Molecular Dynamics Simulations.

We present a method based on kinetic molecular theory that identifies reactions of various molecularities in molecular dynamics (MD) simulations of bulk gases. The method allows characterization of the thermodynamic conditions at which higher than bimolecular reactions are a factor in the mechanisms of complex gas-phase chemistry. Starting with Bodenstein's definition of termolecular collisions we derive analytical expressions for the frequency of higher molecularity collisions.

General application of Tolman's concept of activation energy.

We present a generalization of Tolman's concept of activation energy applicable to thermal and non-thermal reactions in molecular dynamics simulations of reactions in bulk gases. To illustrate the applicability of the method, molecular dynamics calculations were carried out for the NVT ensemble to determine the activation energies of O + H → H + HO and 2O + H → 2HO from MD simulation results for [H]/[O] = 1 at 3000 K using the reactive force field, ReaxFF. Assuming local thermodynamic equilibrium, we define the reaction cluster local energy, the energy of the atoms participating in an individual reaction, which is conserved.

On the role of the termolecular reactions 2O + H → 2HO and 2O + H → H + HO + O in formation of the first radicals in hydrogen combustion: ab initio predictions of energy barriers.

We have investigated the role of termolecular reactions in the early chemistry of hydrogen combustion. We performed molecular chemical dynamics simulations using ReaxFF in LAMMPS to identify potential initial reactions for a 1 : 4 mixture of H : O in the NVT ensemble at density 276.3 kg m and ∼3000 K (∼4000 atm) and ∼4000 K (∼5000 atm), and then characterized the saddle points for those reactions using ab initio methods: CCSD(T) = FC/cc-pVTZ//MP2/6-31G, CCSD(T) = FULL/aug-cc-pVTZ//CCSD = FC/cc-pVTZ and CASSCF MP2/6-31G//MP2/6-31G.