CCL: Is CASSCF appropriate for study of PES?

[errol lewars <elewars:_:trentu.ca>]

 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>
>  ------=_Part_4657_175608.1132432456569-->
>  
>