Re: [ESPResSo-users] Sistematically decreasing of Temperature with DPD thermostat

[Ulf Schiller]

Hi Salvador,

On 01/15/2014 04:11 PM, Salvador H-V wrote:
> So, I have to think more carefully what Stefan said: "Thermalization of
> rotational degrees of freedom is entirely different in Langevin than
> what happens when combining rigid bodies with DPD (this so far probably
> nobody has done)."

You may want to look at Q-DPD. Rigid bodies are already discussed in the 
very first paper on DPD [Hoogerbrugge and Koelman 1993, EPL 21, 363]. 
The question was picked up by Martys and others with regard to 
quaternion algorithms (this now commonly goes under the name 
Q-DPD)[Martys and Mountain 1999, PRE 59, 3733]. A discussion how to 
account for constraint forces can also be found in [Martys 2005, J. 
Rheol. 49, 401-424]. Allow me to reiterate the point first raised by 
Rudolf that it is not clear that ESPResSo's constraint algorithm works 
for the dimensionality of your system.

Also, since your temperature seems to be slightly too high, it may be 
worth checking finite time-step artifacts (in particular as velocity 
verlet is only first order for velocity dependent forces).

Hope that helps,
Ulf

--
Dr. Ulf D. Schiller                        Building 04.16, Room 3006
Institute of Complex Systems (ICS-2)       Phone:   +49 2461 61-6144
Forschungszentrum Jülich, Germany          Fax:     +49 2461 61-3180

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