From owner-chemistry@ccl.net Sun Nov 20 19:19:00 2005
From: "makowskm{}chemia.uj.edu.pl" <owner-chemistry]_[server.ccl.net>
To: CCL
Subject: CCL: Is CASSCF appropriate for study of PES?
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Date: Sun, 20 Nov 2005 10:16:13 +0100 (CET)
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Sent to CCL by: makowskm]![chemia.uj.edu.pl

> Hi CCLers,
>  I am studying the PES of a small molecule and wondering
> whether CASSCF or CASPT2//CASSCF is an appropriate
> method for the PES study since these methods are not
> size consistent. Another downside of using CAS is that there
> is no good way of choosing virtual orbitals into the active space.
>  Any comments?
>  Thanks a lot!
> Yingbin

The statement that they are not size consistent is not true. It depends
how you choose your active space.
If you study A + B = AB reaction size consistency would be kept if active
space for AB is a direct sum of active spaces for A and B.
Yes, this is true that finding active space appropriate for specific
problem  might be a hard work. Point is, if your system is
multiconfigurational in its nature or electronic state changes on scan
surface, CASSCF/CASPT2 or some kind of MRCI might be the only valid
choice.

Yours,
Marcin Makowski

-- 
Dr Marcin Makowski
Jagiellonian University
Department of Theoretical Chemistry
email:makowskm[a]chemia.uj.edu.pl
or
Kyushu University
email:marcin[a]cube.kyushu-u.ac.jp