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

From: Salvador H-V
Subject: Re: [ESPResSo-users] Sistematically decreasing of Temperature with DPD thermostat
Date: Wed, 15 Jan 2014 09:11:28 -0600

Dear All,

Thanks to all of you  for your comments and suggestions.

I have considered all of them and did some tests.

I did different tests and when using the same program and removing the rigid bonds ( i have a 2d system of spheres) the temperature is preserved.  

Also, as Stefan suggested I switch form rigid bonds to harmonic bonds

{ dpd 1.5 0.0 1.122462048309373 WF 1 1.0 1.122462048309373 TWF 1 } 

{0 HARMONIC 1000.0 1.0 1.3} {0 0 lj-gen 1.0 1.0 1.020408163265306 0.1011256571291992 0.0 50  49  134.5526623421209 134.5526623421209 0.0 }

And now the temperature is fluctuating around 1.6$$... I had to use a very high value of K to keep the particle's center distance around 1.0.

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).

I would appreciate any extra comments and suggestions. 

Thanks a lot,


On Wed, Jan 15, 2014 at 7:04 AM, Ulf Schiller <address@hidden> wrote:
On 01/15/2014 09:07 AM, Stefan Kesselheim wrote:
set temp [expr [analyze energy kinetic]/($np)]

Hi Salvador,

how do you calculate $np? Keep in mind that the number of degrees of freedom is reduced by the number of constraints.



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


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
Sección 5A Reserva Territorial s/n, 
Col. Santa Bárbara, 
CP 91096
Xalapa, Ver. Mexico


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