Subject: CCL: Ewald Sums and Amber 1-4 interactions.

From: "Mark Thompson" <mark.-at-.arguslab.com>
Date: Tue, 16 Sep 2003 11:42:35 -0700

I've been examining some old MD code of mine and I believe there is a
problem with how I've handled the scaled 1-4 electrostatic terms in Amber
when treating the long-range electrostatics using the Ewald method.

Amber scales the 1-4 electrostatic terms by a scale factor.  It's unclear to
me how this should be accounted for in the Ewald method.  These interactions
are already included in the k-space sum and usually are corrected for in the
real-space exclusion correction.  Its not clear to me how the scaled-1-4
term can be accounted for other than to do the real-space Ewald treatment of
the 1-4 term and then multiply in the Amber scaling term.

Any ideas, pointers would be appreciated.  I'll summarize for the list.

Cheers,
Mark Thompson

***************************
Mark Thompson, PhD
Planaria Software LLC
PO Box 55207
Seattle, WA  98155
http://www.arguslab.com
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