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

[Salvador H-V]

Hi Ulf,

Thanks a lot for the reference... I will read (again) the original paper of DPD!

Regarding your comment: "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. "

As I previously asked Stefan, this means that using rigid bonds or even harmonic bonds in a 2Dimensional system is not the right thing to do?  How to be sure that using bonds (rigid or harmonic) in a two dimensional system is given unphysical results?

I would really appreciate any extra comments...  

Thanks a lot in advance

Salvador

On Wed, Jan 15, 2014 at 9:47 AM, Ulf Schiller <address@hidden> wrote:

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

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Dr. Salvador Herrera-Velarde
Simulacion Computacional de Materia Condensada Blanda
Sub-Direccion de Investigacion y Posgrado
Instituto Tecnologico Superior de Xalapa (ITSX)
Instituto Tecnológico Superior de Xalapa
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