where t p refers to the plateau time of the flux-side correlation function, and κ(t) is the time-dependent transmission coefficient that captures the dynamical recrossing effects, measuring the ratio between the reaction rate and the TST rate. Since the classical κ(t) always starts from 1 and decays to a finite value (between 0 and 1) at t p , the k TST is the upper limit of the actual rate constant k. Numerically, the transmission coefficient can be numerically calculated from the flux-side correlation function formalism as follows