When a configuration interaction calculation is done, all spin states are calculated simultaneously, either for component of spin=0 or 1/2, unless other keywords which define the spin are present. When only doublet states are of interest, then DOUBLET can be specified, and all other spin states, while calculated, are ignored in the choice of root to be used.
Note that while almost every odd-electron system will have a doublet ground state, DOUBLET should still be specified if the desired state must be a doublet.
See also SINGLET, TRIPLET, QUARTET, QUINTET, SEXTET, SEPTET, OCTET, and NONET.
DOUBLET has no meaning in a UHF calculation.