From:	Patrick Bultinck <Patrick.Bultinck %-% at %-% rug.ac.be>
Date:	Tue, 26 Apr 1994 09:34:22 +0200 (MET DST)
Subject:	Use of symmetry in optimisations

Netters,

I have just sent a reply to a question concerning the use of a Z-matrix
for a calculation on ethylene, using GAMESS (US).

As a direct consequence I rembered something that I am not very
comfortable with...

In section 4 of the GAMESS manual, I find under a title : ***The role of
symmetry*** that it is best to use symmetry during an optimisation.
However GAMESS never lowers the symmetry during an optimisation. It is a
well known fact that sometimes a minimal energy structure differs (a lot)
from the symmetry you might expect. Isn't it then safer to always do
unconstrained optimisations, and if you think that the result differs so
little from a certain symmetry point group, you can always do a
symmetry-optimisation starting from the geometry with that symmetry, and
compare energies...

The most important disadvantage is off course that it often takes a lot
of time to reach a certain symmetry point group, when you start from
zero-symmery.

Any thoughts on this...

Those interested in a summary of some sort should send me a note, if
enough interest exists, I send one to CCL.

Thanks,


|-----------------------------------------------------------------------|
|     C-C                       Patrick Bultinck                        |
|    /   \                      Dept. Physical & Inorganic Chemistry    |
| C-O     O-C                   Section Quantum Chemistry               |
| |         |                   University of Ghent                     |
| C-O     O-C                   Krijgslaan 281 (S-3)                    |
|    \   /                      9000 Gent                               |
|     C-C                       Belgium                                 |
|                               Tel. Int'l code/32/9/264.44.44          |
| Macrocycles                   Fax. Int'l code/32/9/264.49.83          |
| Quantum Chemical              E-mail : Patrick.Bultinck()at()rug.ac.be     |
| Calculations                                                          |
|-----------------------------------------------------------------------|





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