From:	varnai (- at -) bellatrix.pcl.ox.ac.uk (Peter Varnai)
Date:	Wed, 25 Feb 1998 20:59:31 +0000 (GMT)
Subject:	extended electrostatics in CHARMM

Dear CCLers,

"Extended" electrostatic calculation can provide an efficient way to approximate
the total electrostatic interaction. The electrostatic term has two contribution:
1, conventional pairwise summation (spatially close particles)
2, multipole approximation (spatially distant particles)
To reproduce the electrostatic energy calculated without cutoff, one adds the
above
terms. In the first term there is NO smoothing.
Here comes my questions: in CHARMM manual it is written that
"The interactions between particles within CUTNB are truncated
rather than having a SHIFt or SWITch function applied."
Unfortunately, the code uses switch function in the electrostatic calculation.

Does anybody know how to get around this problem?
Does anybody have positive/negative experiences with this model?

Thank you,

Peter Varnai
Oxford University
UK




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