From owner-chemistry@ccl.net Sun Nov 20 13:42:00 2005
From: "errol lewars elewars%x%trentu.ca" <owner-chemistry^-^server.ccl.net>
To: CCL
Subject: CCL: Is CASSCF appropriate for study of PES?
Message-Id: <-30012-051120131117-25829-kc3HqW59mMwSJpvAgqos6Q^-^server.ccl.net>
X-Original-From: errol lewars <elewars:_:trentu.ca>
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Date: Sun, 20 Nov 2005 13:11:28 -0500
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Sent to CCL by: errol lewars [elewars(!)trentu.ca]
2005 Nov 20

If your reaction is A--> B size-consistency (SC) should not be a 
problem. If it is A--> B + C, e.g. the energy of a dimer compared to the 
separated monomers, you have to worry about  SC.

"No good way... virtual orbitals". CASSCF is not a model chemistry (see 
e.g. Foresman and Frisch, "Exploring Chemistry with Electronic 
Structutre Methods", so there in no _automatic_ way to choose the MOs of 
the active space. But people still use CASSCF and get useful results.

E. Lewars
===


Yingbin Ge yingbin.ge^gmail.com wrote:

>Sent to CCL by: Yingbin Ge [yingbin.ge]![gmail.com]
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>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
>
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><div>Hi CCLers,</div>
><div>&nbsp;</div>
><div>I am studying the PES of a small molecule and wondering</div>
><div>whether CASSCF or CASPT2//CASSCF is an appropriate</div>
><div>method for the PES study since these methods are not</div>
><div>size consistent. Another downside of using CAS&nbsp;is that there</div=
>  
>
><div>is no good way of choosing virtual orbitals into the active space.</di=
>v>
><div>&nbsp;</div>
><div>Any comments?</div>
><div>&nbsp;</div>
><div>Thanks a lot!</div>
><div>Yingbin</div>
>
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>
>
>  
>