A orbital diagram of the nomenclature used for CI and MCSCF calculations.


Diagramatically:

       CI       |      RAS      |     CAS
-----------------------------------------------
                | frozen_uocc   | frozen_uocc
dropped_uocc    | rstr_uocc     | rstr_uocc
-----------------------------------------------
                | RAS IV        |
                | RAS III       |
active          |               | active
                | RAS II        |
                | RAS I         |
-----------------------------------------------
dropped_docc    | rstr_docc     | rstr_docc
                | frozen_docc   | frozen_docc


Notations:

uocc           - Unoccupied orbitals.
active         - Variable occupation numbers.
socc           - Singly occupied orbitals.
docc           - Doubly occupied orbitals.


frozen_uocc    - Absolutely frozen virtual orbital.
rstr_uocc      - Can have rotations, no excitations into.
dropped_uocc   - rstr_uocc + frozen_uocc
----- end CI active
RAS IV         - uocc, limited number of excitations into
RAS III        - uocc, limited number of excitations into
RAS II         - docc/socc/uocc, equivalent to active in CAS
RAS I          - docc/socc/uocc, limited excitations out of
----- start CI active
dropped_docc   - rstr_docc + frozen_docc
rstr_docc      - Can have rotations, no excitations from.
frozen_docc    - Absolutely frozen core orbital.

Orbitals are sorted by space, irrep, eigenvalue.
