Re: amber-developers: isotropic periodic sums now in Amber 9

From: David A. Case <>
Date: Fri, 15 Apr 2005 13:28:59 -0700

On Fri, Apr 15, 2005, Wu, Xiongwu (NIH/NHLBI) wrote:

> > Does the IPS have a a surface energy correction (neutralizing
> IPS likes Ewald using images to represent long range interaction, but
> instead of lattice images used by Ewald, IPS uses so called isotropic
> periodic images so that the calculation is much easier. So no surface
> correction is added.

Let me add my (non-expert!) two cents: although there is no "surface
as such, there is a somewhat analogous correction: see Eq. 15b in
paper. I think it is this that (for example) keeps the energy from being
infinite for a charged system (which would be the case for a naive IPS).
So in that sense, this serves some of the same purpose as a background
neutralizing charge.

One of the key things that I want to find out is how IPS performs on
with a net charge. I have free-energy calculations now implemented, so I
should know something soon....

Received on Wed Apr 05 2006 - 23:49:58 PDT
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