Berendsen thermostat

The Berendsen thermostat is an algorithm used in molecular dynamics simulations to control the temperature of the simulated system by rescaling the velocities of the particles. It is named after Herman Berendsen. The method weakly couples the system to an imaginary heat bath held at a target temperature, so that any difference between the system temperature and the bath temperature decays exponentially with a chosen time constant. Because it damps fluctuations of the kinetic energy, it does not generate trajectories that match the canonical ensemble, especially for small systems, although for systems of hundreds or thousands of atoms the results are roughly right for most properties. It is popular because it relaxes a system to the target temperature very efficiently, and simulations are often equilibrated with it before another thermostat such as Nose-Hoover is used to collect data. It can produce the flying ice cube artifact, and the Bussi-Donadio-Parrinello thermostat avoids this, so use of the Berendsen scheme is now recommended mainly for replicating earlier studies.