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16.2.3 Specifying open-shell orbitals

OPEN, $orb_1.sym_1,orb_2.sym_2,\ldots,orb_n.sym_n$

This optional card can be used to specify the singly occupied orbitals. The number of singly occupied orbitals must be equal to spin, and their symmetry product must be equal to sym (see WF card). If the OPEN card is not present, the open shell orbitals are selected automatically. The algorithm tries to find the ground state, but it might happen that a wrong state is obtained if there are several possibilities for distributing the open shell electrons among the available orbitals. This can also be avoided using the CLOSED card. If $orb_i.sym$ is negative, this orbital will be occupied with negative spin (only allowed in UHF).


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