Electronic excitation transfer in Lennard-Jones fluid: Comparison between approaches based on molecular dynamics simulation and the many-body Smoluchowski equation

Molecular dynamics simulations were performed to study the kinetics of long-range irreversible/ reversible electronic excitation transfer in a Lennard-Jones fluid where the translationaly mobile choromophores are thought to be embedded. The simulations are based on the Forster master rate equation approach which can be rederived from a stochastic Liouville formalism for excitation transfer between two identical chromophores in the weak dipole-dipole coupling regime. For energy transfer between two dissimilar partners, rate equations utilized are obtained from the first principle. The simulated kinetic results in this regime are then compared with the reaction-diffusion theoretical framework for excitation transfer. The theory is based on a many-body Smoluchowski equation for the reactant molecule reduced distribution function and makes use of a superposition approximation to truncate the hierarchy of equations. The comparison of the results show the scope and utility of the theoretical approach in the high friction limit when it is solved for the absorbing boundary condition at contact. In the low friction limit, like collisional quenching, the present reaction-diffusion formalism is found to perform poorly. When the stochastic Liouville equation in the strong dipolar coupling regime is solved combined with the molecular dynamics trajectories, the time dependent reaction probability of the donor shows oscillatory behavior and the diffusion coefficient of the medium has been found to have but Little effect on this. (C) 1997 American Institute of Physics.