Blue moon approach to rare events

The Blue Moon ensemble is a computationally efficient molecular dynamics method to estimate the rate constants of rare activated events when the process can be described by a reaction coordinate xi(r), a well-defined function in configuration space. By means of holonomic constraints a number of values of (r) can be prescribed along the relevant path to identify the bottleneck region first and to sample an ensemble of starting conditions to generate activated trajectories. These MD trajectories sample phase space according to a biased configurational distribution. With a suitable re-weighting of averages from such ensemble of trajectories one can characterize completely rare events.