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Re: [ESPResSo] Fwd: setmd skin
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From: |
Axel Arnold |
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Subject: |
Re: [ESPResSo] Fwd: setmd skin |
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Date: |
Fri, 25 Jun 2010 18:46:35 +0200 |
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User-agent: |
KMail/1.10.3 (Linux/2.6.27.45-0.1-default; KDE/4.1.3; x86_64; ; ) |
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, Universität Stuttgart Email: address@hidden
Pfaffenwaldring 27
70569 Stuttgart, Germany