New Developments and Applications of Direct Dynamics Simulations for Gas Phase Reactions

Classical trajectories are propagated using the energy gradient calculated from quantum mechanical methods, through which atomic level chemical dynamics are used to investigate the properties of unimolecular and bimolecular reactions. The program development work involves the improvement of the interface between the classical trajectory simulation program (VENUS) and quantum chemical programs (NWChem and GAMESS) by adding trajectory restart capability and alternate initial SCF guesses. Intramolecular and intermolecular energy was followed along the trajectories to investigate energy partitioning and transferring, e.g., the partitioning between relative translational energy and internal (rotational and vibrational) energy to compare with molecular beam experiments, or the energy transfer between solvent and solute to investigate the solvent affect in chemical reaction. The simulations were performed on the chemical system of dissociation of 1,2-Dioxetian, F- + CH3I SN2 reaction, formation and dissociation of 1,5-Dinitrobiuret and spin-orbital coupling affect of HBr+ + CO2 reaction.