CCL: Transition States



Dear Dr. Sanjay,

it would be much easier to help you if you explained which reaction and mechanism you are trying to model ;-)

Kind regards/Johannes

2009/9/3 CCL CCL computationalchemist%x%gmail.com <owner-chemistry . ccl.net>
Dear Friends,

I am modelling a reaction pathway, using different level of theory, 
say AM1, HF/3-21G, HF/6-31G, B3LYP/6-31G etc.,

When, i use the semi-empirical approach, i could trace all the transition state species in the pathway.
But, when i use the geometry in higher level, say HF and in DFT (B3LYP), i am not getting the
same TSs, as I got in semi-empirical methods, but to the intermediates.

Does that mean there is a change in the mechanism in the reaction, or it is just 
the inability of the DFT to trace the species.

I was suggested to do the single point calculationes for those species using higher level
denoted as (AM1//B3LYP/6-31G) for such a situation.

Could anyone please help me to point out some references, where such situation has been used
reported in the literature, where the single point calculationes at DFT and HF level are carried out
for the TSs obtained over the semi-empirical approaches.

Best regards,
Dr. Sanjay

--
Regards,
Dr. Sanjay Bharathwaj Kumar
Dharmendra Institute of Technology,
Nagapattinam.



--
Adam Johannes Johansson
Ph.D., M.Sc.
Institut für Organische Chemie
RWTH Aachen University
Landoltweg 1
52056 Aachen
Germany
Cell phone:0708178487
E-mail:johjo76 . gmail.com
Research web page:www.physto.se/~johjo