softmatter:Berendsen Thermostat

From NSDL Materials Digital Library Soft Matter Wiki

The Berendsen thermostat maintains temperature by coupling the system to an external heat bath that is fixed at a desired temperature. The heat bath acts to supply or remove heat to/from the system. The basic idea of this is to rescale velocities to achieve a mean kinetic energy consistent with the target bath temperature. The velocities of each particle is rescaled at every time stuff such that:

where τ is a coupling factor whos magnitude determines how tightly the bath and system are coupled.

Key features:

• This method gives an exponential decay of the system towards the desired T.
• The scaling factor for the velocities is:

• If τ is large ( λ ~ 1), coupling is weak.
• If τ is small ( λ is large), then coupling is strong.
• If τ = δt, the algorithm is equivalent to simple velocity rescaling.
• Allows for proportional controll over temperature.
• This allows for fluctuations about the target temperature, while velocity rescaling does not.
• If the system is weakly coupled, the trajectory is nearly identical to an NVE trajectory and is this ok for dynamics.
• Primarily used to prevent long time drift of Energy in an NVE molecular dynamics system.
• DOES NOT reproduce the canonical ensemeble and fluctuations do not correspond to any obvious ensemble.