ACTIVATION-ENERGIES BY MOLECULAR-DYNAMICS WITH CONSTRAINTS

Recently Tobias and Broods introduced a method to compute by molecular dynamics with constraints the probability density P(r approximately) = [delta(r-r approximately)] associated with rate values r approximately of a spatial coordinate r. In this Letter we extend their approach to the case of a general reaction coordinate zeta(r), an arbitrary function of the configuration-space coordinates. The generalized version is shown to be the intergral form of the free energy calculation in the constrained-reaction-coordinate ensemble where the mean force is computed as an average in a zeta-constrained ensemble. The two approaches are shown to be of equal computational efficiency for a very simple Lennard-Jones test case.