Since direct simulation using MD or MC is relatively impractical for improving sampling of sidechain rotamer transitions, given the exponential dependence of barrier-crossing rates on the barrier height, biased or enhanced sampling techniques such as umbrella sampling may be more suited to this problem. Umbrella sampling applies biasing techniques to augment the sampling of selected motions and can be used to enhance sidechain sampling Although it is an efficient tool for generating the free energy landscape (or potential of mean force, PMF) of individual sidechain rotamers, its utility declines as simulations and systems become more complex.