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

```Hi.

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 , 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

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,
Stefan

>
> Best,
> Chunda
>
>

Stefan Kesselheim
Institute for Computational Physics
University of Stuttgart