Subject: Negative eigenvalues in an IRC Calcn!

From: Dave <[email-masked]>
Date: Mon, 06 Jul 1998 12:34:14 +0100

Greetings,

This is my debut on CCL so please excuse my nerves!

I have been doing some ab initio calculations recently on the ring
opening of cyclobutene using GAUSSIAN94.  I have completed an
optimisation of the transition state corresponding to the ring opening
and formation of the TRANS product (trans-butadiene).  To check that the
transition state corresponds to the trans conformation an IRC
calculation was performed to follow the path in the direction TOWARDS
(reverse direction) the trans product. The command line was:

>>  # RHF/6-31G(d) IRC(CalcFC,Reverse,Stepsize=40,maxpoints=24)

The calculation stopped on the 12th point along the path after 5
optimisation steps having failed to converge with this unusual message:

>>   Optimization stopped.
>>      -- Wrong number of negative eigenvalues: Desired=  0 Actual=***

This is very peculiar - I have never seen this before.  It is highly
unlikely that the calculation has 'stumbled upon' another saddle point.
Has anyone come across this before?  Any reasons/suggestions/ideas would
be welcomed.

Thank you for your time,

Dave P.

__________________________________________________________
Dave Pender                                    Tel. 01483 259591
Department of Chemistry                  Pager. 0336 785185
University of Surrey
Guildford
Surrey,  UK
GU2 5XH.

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