Test of a Fokker-Planck-Kramers equation treatment for short-time dynamics of diffusion-controlled reactions by molecular dynamics simulation in Lennard-Jones fluids

We test the extended Harris (EXH) theory for the dynamics of diffusion-controlled reactions using the molecular dynamics simulations in Lennard-Jones fluids. The EXH theory is based on the Fokker-Planck-Kramers equation in which the inertia effect on the molecular migration is taken into account. The time dependence of the theoretical survival probabilities of the reactant agrees with the simulation results if the potential of mean force and the initial equilibrium distribution are appropriately taken into account. The position dependence of the diffusion coefficient is not necessary in explaining the simulation results. On the other hand, the simulation results cannot be reproduced if the two-body or the uniform potentials are employed in the theoretical calculations.