Langevin dynamics is turned on by a nonzero FBETA (friction) array, a nonzero ILBFrq parameter, and an appropriate choice of RBUF. Langevin dynamics represents a coupling of the system to a heatbath and thus provides a means to control and maintain temperatures. A harmonic energy term can be used to restrain the Langevin particles and provide a rough approximation of a potential of mean force.