Subject: Re: CCL:Help with Gaussian error message

From: Connie Chang <cc236)at(ccmr.cornell.edu>
Date: Thu, 17 Jun 2004 15:57:32 -0400 (EDT)

Hi CCLers

Thanks to all those who replied to my question about the Gaussian error I
received:

No NMR shielding tensors so no spin-rotation constants.
| Leave Link  601 at Fri Jun 11 14:36:46 2004, MaxMem=    6291456 cpu: 1.0
|  (Enter C:\g03w\l9999.exe)

I put in the Nosymm keyword and that seems to have fixed the problem.
Benzene as many of you replied tends to want to be symmetric, but when a
charge is placed on it, that symmetry is disrupted and Gaussian needs to
know that.

Pablo Vitoria's reply:

Yes, that's it, the error comes from the fact that Gaussian couldn't
complete the optimization. You can try increasing the maximum number of
optimization steps to N with opt=(maxcycle=N).

Pedro's reply:
Are you trying negative charge? Benzene is not stable with negative charge
and could affect your convergence (it is not a rule though).

Try B3PW91, I usually work with that one and was able to have benzene with
charge -1 converge (although giving a larger energy than the neutral).  I
have never tried charge +1, however it is not difficult to imagine that
you will also get higher energy than for the neutral

And Jarek Panek's reply:

Yes, I guess you have it right - Gaussian exceeded maximum number of steps
(probably earlier you saw message like this below):
!               Non-Optimized Geometry          !
The reason is, as far as my intuition goes, that benzene is highly
symmetric. Now you want to compute the cation, and the cation is probably
not exactly "aromatic" any more! I think the bond lengths will be
no more equal... If they are (see the Non-Optimized geometry in the file),
restart the job with artificially displaced one of the carbon atoms)

Thanks again!

Connie