Re: [ESPResSo-devel] Langevin thermostat (cool/heat)

[Ulf Schiller]

On 24/03/15 14:39, Jakub Krajniak wrote:
> Dear all,
> 
> I have a question on Langevin thermostat, mainly the heat/cool down part.
> 
> Looking into the code:
> https://github.com/espressomd/espresso/blob/master/src/core/thermostat.cpp#L142
> 
> 
> void thermo_heat_up()
> {
> if(thermo_switch & THERMO_LANGEVIN) {
> langevin_pref2_buffer = langevin_pref2;
> langevin_pref2_rotation_buffer = langevin_pref2_rotation;
> langevin_pref2 *= sqrt(3);
> 
> Why pref2 is multiply by sqrt(3), is it some rule of thumb or is there
> any theory after that?
> 
> Could this heat/cool part cause some instability if the integrator is
> restarted too often?

Hi,

The factor sqrt(3) is needed to account for the 'additional' random
noise that is applied when the integrator is restarted. It makes sure
that the variance of two independent half-steps is identical to one full
timestep. I don't think this will cause any instabilities.

Cheers,
Ulf

-- 
Dr Ulf D Schiller
Centre for Computational Science
University College London
20 Gordon Street
London WC1H 0AJ
United Kingdom