  The free energy landscapes of several fundamental processes are characterized
by high barriers separating long-lived metastable states. In order to explore
these type of landscapes enhanced sampling methods are used. While many such
methods are able to obtain sufficient sampling in order to draw the free
energy, the transition states are often sparsely sampled. We propose an
approach based on the Variationally Enhanced Sampling Method to enhance
sampling in the transition region. To this effect, we introduce a dynamic
target distribution which uses the derivative of the instantaneous free energy
surface to locate the transition regions on the fly and modulate the
probability of sampling different regions. Finally, we exemplify the
effectiveness of this approach in enriching the number of configurations in the
transition state region in the cases of a chemical reaction and of a nucleation
process.
