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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.

Axel

-- 
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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