Subject: Summary: geometry optimizations

From: Dale Andrew Braden <[email-masked]>
Date: Fri, 11 Apr 1997 08:05:41 -0700 (PDT)

Dear CCL,

Below is the collection of responses to the following question about
the choice of coordinates for geometry optimizations.  Thanks to all who
responded!

Dale Braden
Department of Chemistry
University of Oregon
Eugene, OR 97403-1253
[email-masked]

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Question:

A brief question:  Are there any circumstances in which a geometry
optimization in Cartesian coordinates would be *faster* than in redundant
internal coordinates? 

The reason I am asking is because I am trying to optimize the geometry of
a hydrogen-bonded dimer in a solvent medium using Gaussian 94, and the
change in the two intermolecular Z-matrix coordinates (distance and angle) 
remains large for many, many iterations.  The geometry isn't exactly
oscillating between two structures, but it isn't settling down, either,
and I thought that perhaps by changing the optimization method from
redundant internal coordinates (the default method in G94) to cartesians,
the optimization might proceed more smoothly to a converged minimum.  I
don't want to try this unless it can work, because the calculation is
expensive. 

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