Subject: Re: SPARTAN: Summary: Symmetry Bug

From: "Kersey Black" <[email-masked]>
Date: Thu, 19 Jun 1997 09:49:09 -0700

On May 11,  4:56pm, Alan Shusterman wrote:
> Subject: SPARTAN: Summary: Symmetry Bug
> The following note summarizes replies and answers I received to my question
> about an apparent symmetry bug in Spartan 4.1.
>
> Here is my original post:
> --------------------------------
> I run into the following bug every few weeks:
>
> I build a molecule with a certain symmetry (Cs in this case) and optimize its
> structure with symmetry ON.  Then I try to reoptimize its structure with a
> larger basis set while still using symmetry, but Spartan stops with the
> following error message:
>

I have truncated the message and rely on memories for some of the details.  It
is ironic that this should cross my desk so recently because I confronted a
similar symmetry problem this morning, however I just discoved while writing
this that it is a feature, and not a bug.  I share the problem with the list
because others may want to know about this if planing to use the DFT methods.

The bottom line is that symmetry when using DFT in 4.1.1 is not supported.
 Also, the use of constraints is not supported.  Thus, I got caught in the
following bind.

I exploited the Cs symmetry of a transition state (C1 ground states) to
effectively constrain it while "geometry optimizing" to a transition state
stationary point with that symmetry.  This approach worked well at the PM3(tm)
level, but when I went to DFT the symmetry was turned off by Spartan and every
thing proceeded as if C1.  As a consequence the structure optimized towards a
ground state structure.

This leaves me trying to find a transition state on a relatively flat surface
using the Transition State option and C1 symmetry.  Wish me luck.

I discover in the on-line help that nosymmetry is the default in DFT.  I hope
that this gets corrected in future versions.  The inability to use symmetry
this way makes calculations much more costly and more difficult, and makes the
DFT options substantially less valuable.

Cheers

Kersey Black

-- 
<::::::::::::::::::::::>
Kersey Black
Associate Professor of Chemistry
Claremont McKenna, Pitzer, Scripps Colleges
925 N. Mills Ave
Claremont, CA  91711-5916
[email-masked]