Subject: geometry optimization and SCF convergence

From: Stephen Little <[email-masked]>
Date: Wed, 2 Aug 95 11:58:13 -0400

Hello CCL,
  I am trying to reduce the ab initio (e.g. rhf/6-31g*) geometry
optimization time in Gaussian 94. Gaussian 94 uses redundant
internal coordinates by default so the set up of the z-matrix
is not so much of an issue. My question (which I have also
posted to [email-masked]) is whether adjustable SCF convergence
criteria exist for geometry optimization in general. My question to the
list applies to all quantum mechanical geometry optimization.

It seems to me that a precise SCF convergence is wasteful of time
in the initial stages of geometry optimization when the geometry
is relatively crude, since the hamiltonian may have to be 
significantly altered in succeeding geometry optimization steps.
It would seem that some changing value such as one-tenth the
energy between steps in the geometry optimization would make
more efficient use of the SCF cycles. 

If anyone has some more experience in this matter or would like
to responde to flaws to my logic, please respond to me and I will
post a summary to the list.

Thanks for your assistance.

Stephen Little   [email-masked]   

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*    Stephen Little          [email-masked]                 *
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