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Re: [ESPResSo-users] Global Potential in Espresso

From: Axel Arnold
Subject: Re: [ESPResSo-users] Global Potential in Espresso
Date: Thu, 19 May 2011 18:29:37 +0200
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On Thursday 19 May 2011 17:45:39 Peter Kosovan wrote:
> Hi Lorenzo
> You can use part command to set external force acting on particles which
> could simulate a uniform external field. This should do for gravity, if
> your systems are not so huge that you would have to care about the
> curvature of the Earth.
> If you need an arbitrary inhomogeneous external field, to my knowledge this
> is not implemented.

Well, in fact there is something like this, namely the constraints. That 
external potentials, which most have the form of a geometric obstacle, but 
there are also other ones, e.g. the potential generated by a charged rod or 

Since very likely the existing shapes are not what you need, you would need to 
modify constraint.[ch] and interaction_data.h to implement your own shape of 
potential. Just take the plate or rod form as an example, then it should be 
fairly straight forward. If your external potential has a fairly generic form, 
like a harmonic potential, it would be kind if you could send back the code. 
We can then incorporate it into the next release for everybody to use. Plus, 
you can easily switch to newer releases later.

Note that the implementation needs to be in C, since a) Tcl would be painfully 
slow to use during the integration and b) Tcl is only available on the master 
node, but not the rest in a parallel run.

Many regards,

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

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