From owner-chemistry@ccl.net Thu Sep 3 14:35:00 2009 From: "Johannes Johansson johjo76 * gmail.com" To: CCL Subject: CCL: Transition States Message-Id: <-40162-090903143308-28968-YdLAKeclsz81pc6UEe4i3A{}server.ccl.net> X-Original-From: Johannes Johansson Content-Type: multipart/alternative; boundary=000e0cd240bcc01e170472b02906 Date: Thu, 3 Sep 2009 20:00:47 +0200 MIME-Version: 1.0 Sent to CCL by: Johannes Johansson [johjo76{:}gmail.com] --000e0cd240bcc01e170472b02906 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable 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 > 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 a= nd > 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. > --=20 Adam Johannes Johansson Ph.D., M.Sc. Institut f=C3=BCr 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 --000e0cd240bcc01e170472b02906 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable 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 <ow= ner-chemistry . ccl.net>
Dear Friends,

I am modelling a reaction pathw= ay, using different level of theory,=C2=A0
say AM1, HF/3-21G, HF/= 6-31G, B3LYP/6-31G etc.,

When, i use the semi-empi= rical approach, i could trace all the transition state species in the pathw= ay.
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 meth= ods,=C2=A0but to the intermediates.

Does that mean= there is a change in the mechanism in the reaction, or it is just=C2=A0
the inability of the DFT to trace the species.

I was suggested to do the single point calculationes for those species us= ing higher level
denoted as (AM1//B3LYP/6-31G)=C2=A0for such a si= tuation.

Could anyone please help me to point out some reference= s, 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 Jo= hansson
Ph.D., M.Sc.
Institut f=C3=BCr Organische Chemie
RWTH Aach= en University
Landoltweg 1
52056 Aachen
Germany
Cell phone:0708= 178487
E-mail:johjo76 . gmail.com<= br>Research web page:www.physto.se/= ~johjo

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