From owner-chemistry@ccl.net Fri Jun 20 16:09:01 2008
From: "Frank Neese neese^thch.uni-bonn.de" <owner-chemistry,server.ccl.net>
To: CCL
Subject: CCL: Triplet transition states
Message-Id: <-37219-080620160100-22473-vT9UqPQ0dFwthJqJeFZvaw,server.ccl.net>
X-Original-From: Frank Neese <neese : thch.uni-bonn.de>
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Date: Fri, 20 Jun 2008 22:00:41 +0200
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Sent to CCL by: Frank Neese [neese.:.thch.uni-bonn.de]
Dear Gary,

i think that Aurora has made some very nice comments that i fully 
support. I also suggest to read the early papers by Lou Noodleman that 
are important and very useful (e.g. L. Noodleman, J. Chem. Phys. 1981, 
74, 5737;    L. Noodleman, E. J. Baerends, J. Am. Chem. Soc. 1984, 106, 
2316;  L. Noodleman, E. R. Davidson, Chem. Phys. 1986, 109, 131; 
Aurora's papers with Ernest Davidson are also very worthwhile reading, 
e.g.   A. E. Clark, and E. R. Davidson, J. Chem. Phys. (2001), 115, 
7382-7392. and if you allow me to quote this you can also find an 
interpretation of the physical content of the BS solution in F. Neese, 
J. Phys. Chem. Solids 2004, 65, 781).

The procedure she suggests for generating the broken symmetry solutions 
appears to be quite complicated. hence i just wanted to mention that in 
orca (free at http://www.thch.uni-bonn.de/tc/orca/) you get these broken 
symmetry states easily and reliably by simply using:

%scf brokensym 1,1
         end

much more complicated broken symmetry states with several open-shell 
metal ions are also readily found with only a minimum of user input.

Transition states can be readily located using eigenvector following.

If you don't find a transition state on the singlet surface that is 
there on the triplet surface then i am very reminded on the very nice 
work on two-state reactivity, e.g.

S. Shaik, D. Danovich, A. Fiedler, D. Schröder, and H. Schwarz 
"Two-State-reactivity in Organometallic Gas Phase Ion Chemistry". 
_Helvetica Chem. Acta,_  _78_, 1393-1407 (1995).
or nice work also by Jeremy Harvey, e.g. Spin-Forbidden Reactions in 
Transition-Metal Chemistry Jeremy N. Harvey In /Computational 
Organometallic Chemistry/, Thomas R. Cundari, ed., Marcel Dekker, 2001.

If your state is such that a 2 in 2 CASSCF is enough you can also use 
CASSCF in a very straightforward manner to locate your transition state 
(in orca not much more is needed then %casscf nel 2 norb 2 mult 1 end)

Good luck!

Frank

-- 
---------------------------------------------------------------
Prof. Dr. Frank Neese
Lehrstuhl fuer Theoretische Chemie
Universitaet Bonn
Wegelerstr. 12
D-53115 Bonn, Germany
neese|,|thch.uni-bonn.de
Phone: +49-28-732351
FAX: +49-(0)228-739064
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