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

[Peter Knowles]

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.

Peter

On 7 Dec 2010, at 15:52, Eryin Feng wrote:

> Dear Molpro developers and users,
> I am trying to calculate the interaction energy of He-CN(X 2Sigma,ground electronic state) complex. The calculation is performed in Cs point group.The wave function which asymptotically correlates to CN(X 2Sigma)+He system is of 2A' symmetry. The CN(A2Pi)state lies approximately 9250 cm−1 above the X state. In the presence of the He atom, the degeneracy of CN(A2Pi) state is lifted, giving rise to two adiabatic electronic states, of A' and A'' reflection symmetry. The two 2A' states, which correlate at large R to CN(X) and CN(A), mix strongly when the CN bond is stretched slightly beyond its equilibrium distance.So,I must carry out complete-active-space, selfconsistent field (CASSCF) calculations for the lowest three electronic states, two of 2A' and one of 2A'' symmetry. The lowest A' state is mainly dominated by a configuration( its coefficient greater than 0.9),and a single-reference description is valid. I thus want to do the RCCSD(T) calculation following the CASSCF. I try to do as:
>  
>  
> {rhf;occ,7,1}
> {casscf; occ,8,1;  wf, 15,1,1;state,2 ;  wf, 15,2,1}
> {Rccsd(t); occ,8,1; wf,15,1,1 }
>  
> But the Error message: invalid orbital type for Mpn or triples: natural.
>  
>  How do I read orbitals from the  preceding CASSF calculation ?
>  
> Can you give me some suggestions?
>  
> thanks in advance!
>  
>  
> Eryin Feng
>  
> department of physics,
> Anhui normal university,China
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