Subject: SUGGESTION ABOUT TS OPTIMIZATION

From: "E. Lewars" <[email-masked]>
Date: Sat, 28 Feb 1998 16:19:07 -0500 (EST)

1998 Feb 28
Ken Legendre wrote:

                 27-FEB-1998 18:45:26.52
>From:  IN%"[email-masked]"  "Ken Legendre"
To:	IN%"[email-masked]"
CC:	
Subj:	CCL:G:Transition State calculations

Dear CCLers

Hello. I am trying to calculate transition states, using the tight
option in Gaussian 94, at very high levels of theory, and having
problems. I have tried the TS command and get a wrong number of
eigenvlaues error. I have also tried the QST2 and QST3 and get results
but the calculation does not converge. I also used the maxcycle command
in order to give the QST2 and QST3 calculations more cycles to converge.
The program quits after 100 cycles, even when the number of cycles is
set to larger number of cycles. Im not sure why at this point it is
doing that. I have also tried the calcall command and also get the wrong
number of eigenvalues. I would appreciate any suggestions.

Thanks in advance
Kenneth Legendre
[email-masked]
Illinois State University 
Department of Chemistry
Normal, Il 61761
==============

1)  Use the keyword  NoEigenTest.  In my experience Gaussian almost never finds
the TS if it has to check the number of negative eigenvalues of the Hessian.
When you get a putative TS, you can check it out in a separate frequency
job for the number of Hessian eigenvalues (the number of imaginary freqs
in a freq calc).

2)  Find the TS at a lower level of theory and use that structure as input,
requesting a HF calculation to get an initial Hessian.

3)  A TS that exists at one level of theory may not at another level.
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          E. Lewars

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