AMBER Archive (2006)

Subject: Re: AMBER: counterions and particle-mesh-ewald

From: David A. Case (
Date: Wed Aug 30 2006 - 15:14:40 CDT

On Tue, Aug 29, 2006, cristian obiol wrote:
> I have performed some molecular dynamics without neutralizing the system ( no
> counterions ) and using periodic boundary conditions with particle-mesh-ewald
> method.
> It's correct a dynamics with PME and without counterions ??

There is no formal requirement that a PME simulation be neutral; if it is not,
there is an effective uniform "plasma" of charge that provides the

In principle, explicit counterions are a more physical representation of the
underlying reality. In practice, many (most?) simulations do not sample
enough to really average over all the energetically accessible counterion
configurations. In that case, using a plasma might actually be better than
using explicit counterions. I don't know that there is any general rule that
can be drawn here.

Others with good experience, or who have read the literature better than I
have, might chime in here.


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