RHF interpretation: The desired spin-state is a sextet: the state with component of spin MS = 5/2 and spin S = 5/2. In order to define this type of calculation other keywords must also be used. For a 'simple' sextet calculation, use C.I.=5.
When the configuration interaction calculation is done, all microstates having a component of spin, MS, equal to 5/2 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 5/2 can be constructed. From this set, only a sextet state can be selected; all other states will be ignored. If ROOT=n is present, then the n'th sextet state will be selected; otherwise, the first sextet state will be chosen.
If several sextets are to be calculated, say the second or third, then C.I.(n1,n2) should be used.
See also SINGLET, DOUBLET, TRIPLET, QUARTET, QUINTET, SEPTET, OCTET, and NONET. UHF interpretation: The system will have five more alpha electrons than beta electrons.