Define CASSCF active space

[Nastasia Mauger]

Hello,

I am attempting to run a CASSCF calculation with MOLPRO on CO₂⁺ using different active space. The electronic configuration is as follows:

(1σu)²(1σug)²(2σg)²(3σg)²(2σu)²(4σg)²(3σu)²(1πux)²(1πuy)²(1πgx)²(1πgy)¹(2πux)⁰(2πuy)⁰(5σg)⁰.

I would like to define my CAS space as: (1πgx)²(1πgy)¹(2πux)⁰(2πuy)⁰.

According to the manual, I have set up the CASSCF input as follows:

{casscf
occ, 4, 1, 1, 0, 3, 1, 1, 0
closed, 4, 1, 1, 0, 3, 0, 0, 0
wf, 21, 7, 1, 1
select
con, 2, 1, 0, 0
noextra
iprint, civector, pspace, orbitals, natorb, step }

However, the output indicates that only one orbital is used:

  P-space for symmetry 7
 ======================
             CI         Config           Diag
              1            2 /    -4.31775881

 CI Coefficients of symmetry 7
 =============================

 2 /            1.00000000

 Energy:     -187.21371422

It appears that I am unable to define a 3-electron, 4-orbital active space as intended. Despite following the manual, I cannot achieve the desired configuration.

Any help or suggestions on how to properly set this up would be greatly appreciated.

---

[Peter Knowles]

What you have in your input has only the 1\pi_g orbitals in the active space, ie 3 in 2. How about

occ,4,2,2,0,3,1,1

followed by

con,0,0,2,1

?

Peter

On 27 Feb 2025, at 05:33, Nastasia Mauger <nastasia...@gmail.com> wrote:

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