Subject: G94:help with IRC

From: "Dale A. Braden" <[email-masked]>
Date: Wed, 13 May 1998 15:59:24 -0700 (PDT)

Dear CCL,

I've optimized the geometry of a benzenoid molecule to a first-order
saddle point using G94, but I want a true minimum energy geometry.  I've
tried moving the nuclei in the direction of the normal mode corresponding
to the imaginary frequency, but the DFT/SCF process fails.  Now I'm trying
using the IRC method, but this has always failed in the past, and is
failing again now.  The problem is that the default options for this
method in my experience always cause the displacements to become huge, and
in any case the geometry never converges. 

I've also tried using a stepsize of 0.02 au in conjunction with VeryTight
convergence, but this took many steps to optimize the geometry of the
first structure, and the final energy was higher than that of the starting
geometry.  What's the trick with using IRC?

Best wishes to all,

Dale

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