Metadynamics  is a computational method aimed at enhancing the sampling of the configurational space. To achieve this it adds a time dependent repulsive bias potential function of coarse-grained variables, called collective variables. This bias descourages the system from revisiting already sampled configurations.
This method makes possible the estimate of the free energy surface of systems that are not tractable in reasonable computer time with regular unbiased molecular dynamics.
Over the years many improvements to Metadynamics have been proposed, and it has been applied to a variety of different problems. 
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