Efficient trajectory simulation methods for diffusional barrier crossing processes

Abstract

The kinetics of many chemical and biochemical processes in solution are governed by the rate at which systems diffuse across energy barriers separating reactant and product states. These rates can be determined by computer simulation of diffusional trajectories by Brownian dynamics techniques. Conventional simulations, in which systems are dynamically unconstrained, sample barrier crossing events inefficiently since the system spends most of its time in low‐energy configurations. New techniques, termed activated and branching‐activated trajectory methods, are explored which circumvent this problem by constraining trajectories to the barrier top region. The accuracy and efficiency of these new methods are tested by application to a one‐dimensional model chemical system. Activated and branching‐activated results for the rate constant are found to converge 10 to 25 times more rapidly than the conventional first passage time method, even for a modest barrier height of 2k_BT. Application to more realistic multidimensional systems is discussed in an appendix.