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Re: [ESPResSo] basic details:

From: Olaf Lenz
Subject: Re: [ESPResSo] basic details:
Date: Thu, 26 Jul 2007 13:45:09 +0200
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Please note that ESPResSo is not a commercial product, but a program
written and maintained by scientists that are mostly not paid for
answering questions, but do so voluntarily. Therefore, if you want to
get a reply, please try to sound a bit more friendly in your emails.

I have already answered your question in a mailing on July 2nd, subject:
"Re: why does this not appear in the threads". For you convenience, I
repeat it here:

"The important thing in ES is, that it does not have any built-in scale.
A length of '1' can mean a nanometer, an Angström, or a kilometer -
depending on the system that you have in mind. It all depends on the
interaction parameters that you are using. When you create particles
that are intended to represent atoms, then you will probably use a
length scale of Angström und set the LJ parameter sigma to the VDW
radius of the atom in Angström. Or you just set the sigma to 1 and
measure all length in units of the VDW radius. The choice is yours.
The second choice that you have is the energy scale (or time scale). You
can use the VDW-binding energy of two atoms as the energy unit, i.e. you
would set the LJ parameter epsilon to 1, or you set it to x kJ/mol -
again, the choice is yours.
You just have to be aware that you use consistent units throughout all
of the simulations, then everything is fine."

If you feel that this doesn't help, please refer to standard literature,

Mike P. Allen and Dominik J. Tildesley. Computer Simulation of
Liquids. Oxford Science Publications. Clarendon Press, Oxford, 1
edition, 1987.


Daan Frenkel and Berend Smit. Understanding Molecular Simulation.
Academic Press, San Diego, second edition, 2002.

Best regards
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