# [molpro-user] Selection of certain orbitals to correlate

Quan Phung manhquank9 at gmail.com
Fri Oct 31 21:18:24 GMT 2014

```Dear Molpro users,

Let say I have HF orbitals of a molecule and I want to to CCSD(T) of this
molecule.
Now I would like to correlate just some orbitals. including some valance
(but not all valance) and some low-lying core orbitals. So I have to rotate
the core orbitals with the valance orbitals that I do not want to correlate
and do only one iteration. For example:

{hf
wf,108,1,0
shift,-1.0,-0.5
maxit,1
start,2101,2
closed,18,9,9,3,9,3,3,0
occ,   18,9,9,3,9,3,3,0
rotate,9.1,16.1,90
rotate,4.2,9.2,90
rotate,4.3,9.3,90
rotate,4.5,9.5,90

}

where 9.1, 4.2, 4.3, 4.5 are core orbitals and 16.1, 9.2, 9.3 and 9.5
are valance orbitals that I do not want to correlate.

After that I do a CCSD(T) calculation based on this HF calculation.

{ccsd(t)
core,16,9,9,2,9,2,2,0
maxit,50
shift,1
}

I would like to ask if it is make sense to do this?

I also notice that after rotation and do the HF calculation, the core
orbitals (9.1, 4.2, 4.3, 4.5)  are now high-lying and have the energy
equal the the energy of the valence orbitals that were rotated. I am
not sure if this is correct. To be clear:

Before rotation (full HF calculation):

ORBITAL  9.1 (core)    eig=   -4.4491
ORBITAL 16.1 (valance) eig=   -0.9945

After rotation, HF one iteration:

ORBITAL  9.1 (valance)  eig=   -4.4491
ORBITAL 16.1 (core)     eig=   -0.9945

Best regards,

Quan
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