The Andersen thermostat is a proposal in molecular dynamics simulation for maintaining constant temperature conditions.
For each atom or molecule, the reassigned velocity is picked randomly according to Maxwell–Boltzmann statistics for the given temperature.
The thermostat is named after chemist Hans C. Andersen [de] from his 1980 work on the topic.
At each time step of the molecular dynamics simulation, a number of particles are selected to undergo "thermalization".
Due to this interaction with a bath, the system conserves neither energy nor momentum.
In addition, the velocity autocorrelation function decays more quickly than it would in a real system, due to the random decorrelation of the particles.