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From: Olaf Lenz
Subject: [ESPResSo] Re: BOND_CONSTRAINT (Rattle)
Date: Fri, 31 Aug 2007 12:12:19 +0200
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Hi Christopher!

Christopher Jesudason wrote:
> Coming back to the constraint feature, I think that in
> polymers ti would be advantageous to include fixed
> bonds. To set the polymer, the usual command is
> something like this :
> polymer 1 $l_poly  $R_link start $i  charge $Q_D
> distance 1 types 1 1 
> Do I put BOND_CONSTRAINT just beside types 1 1 ?

BOND_CONSTRAINT is a feature, that has to be compiled into the
ESPResSo-kernel, i.e. you have to put it into myconfig.h.

I notice, that so far, there seems to be absolutely NO documentation on
the feature whatsoever, besides the fact that the feature exists.
Unfortunately, Arjit, the original developer is not really accessible
any more.

After I have looked into the source code, I now know that to use it, you
can use a special bond type:

inter <bond_type> rigid_bond <constrained_bond_distance>
<positional_tolerance> <velocity_tolerance>

I do not know whether the feature is tested and how well it works, so I
wish you good luck with it! I would be happy if you could give us a
report whether it works or not.

> Constraints would certainly mean that  much larger
> time steps can be  used, and therefore practicable
> convergence achieved. If you could just write down I
> line of code that can introduce a slinky chain  that
> you know, that would be a very great assistance.

I would hope that the feature does exactly what you want, so just try
it, it might solve your problem.

Good luck!

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