RHF interpretation: The desired spin-state is a quintet: that is, the state with component of spin MS = 2 and spin S = 2. In order to define this type of calculation other keywords must also be used. For a 'simple' quintet calculation, use C.I.=4.
When the configuration interaction calculation is done, all microstates having a component of spin, MS, equal to 2 are selected. These microstates are then used in the construction of states. Because of the way in which the microstates were chosen, only states of spin equal to or greater than 2 can be constructed. From this set, only a quintet state can be selected; all other states will be ignored. If ROOT=nis present, then the n'th quintet state will be selected; otherwise, the first quintet state will be chosen.
See also SINGLET, DOUBLET, TRIPLET, QUARTET, SEXTET, SEPTET, OCTET, and NONET.
UHF interpretation: The system will have four more alpha electrons than beta electrons.