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Re: [ESPResSo-users] About electrohydrodynamics

From: Stefan Kesselheim
Subject: Re: [ESPResSo-users] About electrohydrodynamics
Date: Wed, 31 Aug 2011 06:43:56 +0200


Am 30.08.2011 um 23:46 schrieb Chunda Zhou:

> Hi Guys, 
> My system is a polyelectrolete chain in salt solution with external electric 
> field.
> From the users guide, one can assign an overall electric field. setmd mu_E 
> μEx μEy μEz. Does it mean, this simply assigned the velocity of the charged 
> objects? If yes, then assume I have two charged particles under the external 
> field. In this case, is the velocity of each particle a function of μE or a 
> function of  μE and the electric field of the other particle? 

The first: There is no concept of external electric fields in espresso, and 
thus the input quantity mu E determines the velocity that a particle will have 
at the end of the day. That is why we called that quantity muE because it 
supposed to be the product of the two :-).
> In the literature [19], F-ξ(v-μE)=0. ξ is drag coefficient. Is there a way to 
> assign different drag coefficients for different objects? Or all the objects 
> share the same coefficient which is one? 

The drag coefficient is the lattice-boltzmann friction coefficient, given in 
the command.
lbfluid [...]  friction $gamma

All particles have the same friction coefficient. To implement different 
friction coefficients for different particles is a bit of work, but might be 
desirable for the general usage of LB in general, too, and thus should be 
implement in a general way. If you need it, please contact me.

If you have any more trouble with the implementation, please contact me, too. 
We have tested it, and is not that complex, but I think you are one of the 
first people to actually use it :-).

Cheers and good luck,

> Best,
> Chunda

Stefan Kesselheim
Institute for Computational Physics
University of Stuttgart

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