From owner-chemistry@ccl.net Sat Oct 27 02:16:00 2007
From: "Simon Halstead joyjoyhappyjoy__yahoo.co.uk" <owner-chemistry-.-server.ccl.net>
To: CCL
Subject: CCL: MD of systems with a net charge using Ewald
Message-Id: <-35499-071026230900-23995-DnuH/nru16e1eQu9YEKBUw-.-server.ccl.net>
X-Original-From: Simon Halstead <joyjoyhappyjoy~!~yahoo.co.uk>
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Date: Fri, 26 Oct 2007 19:08:47 -0700 (PDT)
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Sent to CCL by: Simon Halstead [joyjoyhappyjoy#%#yahoo.co.uk]
By the energy I mean the energy of the isolated ion.
My system has a single ion solvated in N SPC/E water.
I obtain the energy of the isolate ion from the
potential energy of the system minus the potential
energy of N water (calculated separately). It is this
energy of a single isolated ion that shows strong
system size dependence.



--- "Konrad Hinsen hinsen+/-cnrs-orleans.fr"
<owner-chemistry]~[ccl.net> wrote:

> 
> Sent to CCL by: "Konrad  Hinsen"
> [hinsen#cnrs-orleans.fr]
> On Oct 26, 2007, at 5:28, Simon Halstead
> joyjoyhappyjoy * yahoo.co.uk wrote:
> 
> > I am running MD simulations on systems with either
> a net +1 or -1 charge using Ewald summation
> > and dl_poly. The Ewald summation should correct
> for the net charge by adding a smeared charge
> > over the cell. However, my results show a serious
> system size dependence for the potential energy
> > (from the coulomb term).
> > Does anyone know of any way to correct the energy
> results?
> 
> Ewald summation does indeed add a neutralizing
> background charge density, which makes the 
> electrostatic energy finite. However, the energy
> depends on the system size. If you think that in
> your 
> specific case the energy should not depend on system
> size, then please tell us why.
> --
>
---------------------------------------------------------------------
> Konrad Hinsen
> Centre de Biophysique Molculaire, CNRS Orlans
> Synchrotron Soleil - Division Expriences
> Saint Aubin - BP 48
> 91192 Gif sur Yvette Cedex, France
> Tel. +33-1 69 35 97 15
> E-Mail: hinsen-.-cnrs-orleans.fr
>
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> 
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