Subject: Re: CCL:Symmetry and Gaussian

From: Bernd Schubert <bernd-schubert^at^web.de>
Date: Thu, 30 Oct 2003 15:22:06 +0100

On Wednesday 29 October 2003 15:58, Raymond C. Fort Jr. wrote:
> I'm sure this has been asked before, but the list archives currently are
> not very searchable.  I've been running some optimizations of small
> molecules with G98 (ethylene, formaldehyde; Cartesian input) to illustrate
> use of the program to a class.  The calculations fail rapidly with the
> message that there has been a change in point group or standard
> orientation.  So far, the only way I can get a calculation to finish is to
> turn off symmetry.  I'd appreciate suggestions of alternatives.
>
> Ray

Hello Raymond,

about 2.5 years ago this has been discussed and a patch has been sent to the 
list. Since I also patched our gaussian that way, I created a readme-file in 
the gaussian-directory that contains some parts of that mail and the patch 
(see attachement).

Hope it helps,
	Bernd

-- 
Bernd Schubert
Physikalisch Chemisches Institut / Theoretische Chemie
Universität Heidelberg
INF 229
69120 Heidelberg
e-mail: bernd.schubert^at^pci.uni-heidelberg.de

---

From: elewars <elewars)at(trentu.ca>
Date: Thu, 30 Oct 2003 11:27:36 -0500

Hello,

If you use input with the symmetry that the optimized product will have, you
should not have this problem. For simple molecules one usually knows what this
symmmetry will be, e.g. H2CO with C2v input should optimize smoothly within this
sym to give a C2v output geometry. I don't know how you get your input geometries;
maybe the problem lies there.

Occasionally it's hard to get exactly the input sym you want; in those cases
Sym=Loose (with Gaussian) may help, or you may be able to hand-edit a small
Cartesian file to the exact sym it should have.

One should always try to optimize within the maximum "expected" symmetry; the
presence of imaginary frequencies will tell you if you have to repeat at a lower
symmetry.

EL
=============

"Raymond C. Fort Jr." wrote:

> Professor Ray Fort Jr.                          Voice: (207)-581-1180
> Department of Chemistry                 FAX: (207)-581-1191
> University of Maine                             EMail: rcfort)at(maine.edu
> Orono, ME 04469                         Web:
> chemistry.umeche.maine.edu/fort.html
>
> Molecular modeling of organic and biological molecules; chemistry of lignin
> and cellulose
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