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Re: [ESPResSo] Fwd: setmd skin

From: Axel Arnold
Subject: Re: [ESPResSo] Fwd: setmd skin
Date: Fri, 25 Jun 2010 18:46:35 +0200
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On Friday 25 June 2010 18:05:51 Mikheil Azatov wrote:
> Thanks everyone especially Axel for explaining, it helped out a lot.
> I still have one question about your answer Axel though. You wrote the half
> step "drag force" as F= -gamma*mass*v/2. I don't understand why you have a
> mass in the friction force. The Langevin equation that I saw in many books
> looks like m*a=F - gamma*v+Fb. Fb beeing a random force

ESPResSo uses a Langevin thermostat to obtain an NVT ensemble, and in this 
case one has m*a= F - gamma*m*v + sqrt(m)*Fb, which is what we have 
implemented in ESPResSo.

Of course,  one would like to have independent friction coefficients for each 
particle, but that is not implemented so far unfortunately.


JP Dr. Axel Arnold Tel: +49 711 685 67609
ICP, Universit├Ąt Stuttgart      Email: address@hidden
Pfaffenwaldring 27
70569 Stuttgart, Germany

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