Subject: rigid vs relaxed scan in Gaussian

From: "Victor M. Rosas Garcia" <[email-masked]>
Date: Wed, 29 May 1996 10:26:48 -0400

Hi there,
	I'm trying to calculate a bond stretching constant for molecular
mechanics work.  I'm doing a Scan of the potential energy surface (well, curve
in this case) for the stretching of the bond with the 6-31+G* basis set in
Gaussian94.  The problem is that the keyword "Scan" in gaussian has two
options: rigid and relaxed.  What is the recommendation for this kind of
parametrization work?  Should the scan keep the molecule rigid or let it relax
at each point of the stretch?  My boss says that it should be relaxed while I'm
going for the rigid.  I think that letting the molecule relax at each point
would make the constant too specific for the model compound and, thus, not of
general applicability; not to mention cross-contamination by other stretches
and torsions present in the molecule.
Any comments are appreciated.

Thanx

Victor.

-- 
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Victor M. Rosas Garcia                   * "How can we contrive to be 
[email-masked]                *  at once astonished at the  
Virginia Tech doesn't necessarily share  *  world and yet at home in it?"
the opinions you just read.	         *  G. K. Chesterton
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