[molpro-user] May the RCCSD(T) read orbitals from the preceding CASSF calculation ?

[Tatiana Korona]

On Mon, 13 Dec 2010, Gerald Knizia wrote:

> On Monday 13 December 2010 11:28, Peter Knowles wrote:
>> Yes, this can be done:
>>
>> {rhf;occ,7,1}
>> {casscf; occ,8,1;  wf, 15,1,1;state,2 ;  wf, 15,2,1}
>> {Rccsd(t);orbital,ignore_error; occ,8,1; wf,15,1,1 }
>>
>> ... although I would consider it to be inadvisable since the (T) correction
>> assumes that the reference wavefunction is RHF.
>
> I'm just wondering: Doesn't UCCSD(T)/RCCSD(T) make semi-canonical orbitals for
> the triples correction? If yes, would this assumption still be a problem?
> -- 
> Gerald Knizia

Gerald,

I think it will still be a problem, since even if the CCSD(T) program calculates 
the (T) correction ignoring the fact that the orbitals are not canonical, this 
will be not the _true_ (T) correction any more, so one will have some sort of a 
new CASSCF-CCSD(T) model of an unknown quality. It is a similar problem as with 
utilizing localized orbitals in LCCSD(T).

Best wishes,

Tatiana

Dr. Tatiana Korona http://tiger.chem.uw.edu.pl/staff/tania/index.html
Quantum Chemistry Laboratory
University of Warsaw
Pasteura 1, PL-02-093 Warsaw, POLAND


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