  Computing reactive trajectories and free energy (FE) landscapes associated to
rare event kinetics is key to understanding the dynamics of complex systems.
The analysis of the FE surface on which the underlying dynamics takes place has
become central to compute transition rates. In the overdamped limit, most often
encountered in biophysics and soft condensed matter, the Kramers' Theory (KT)
has proved to be quite successful in recovering correct kinetics. However, the
additional calculation to obtain rate constants in complex systems where
configurational entropy is competing with energy is still challenging
conceptually and computationally. Building on KT and the metadynamics
framework, the rate is expressed in terms of the height of the FE barrier
measured along the minimum FE path and an auxiliary measure of the
configurational entropy. We apply the formalism to two different problems where
our approach shows good agreement with simulations and experiments and can
present significant improvement over the standard KT.
