quantum_package

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If you want to do a selected CI calculation in a space containing the CAS-CI and all singles and doubles on top of it, you need to define different classes of MOs. This is done using the qp_set_mo_class program.

Here is an example for F_2 in the cc-pVTZ basis set, using Hartree-Fock MOs. We want to freeze the first 2 MOs, use the MOs 7 and 10 as the active space and make all singles and doubles on top of it:

$ qp_set_mo_class -core "[1,2]" -inact "[3-6,8-9]" -act "[7,10]" -virt "[11-60]" f2.ezfio
Core     : (1, 2)
Inactive : (3, 4, 5, 6, 8, 9)
Active   : (7, 10)
Virtual  : (11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60)
Deleted
0000000000000000000000000000000000000000000000000000001111111100
0000111111111111111111111111111111111111111111111111111001000000
0000000000000000000000000000000000000000000000000000001111111100
0000111111111111111111111111111111111111111111111111111001000000
0000000000000000000000000000000000000000000000000000001111111100
0000111111111111111111111111111111111111111111111111111001000000

Now you can run qp_run cas_sd to make the CIPSI selection in the CAS+SD space.

Warning #1: If you run qp_run save_natorb, the order of the MOs may change. The active MOs will be placed between the inactive and the virtual, so you may need to re-define the classes of the MOs with the new ordering.

Warning #2: If you want to do a Full-CI after, you will need to re-set the MO classes such that you don’t have inactive and virtuals MOs. The simplest way is to run qp_set_frozen_core.py. This program runs qp_set_mo_class with an automatically selected valence Full-CI space.

CAS-SD calculations are the starting point of MR-CCSD calculations.