RHF interpretation: The desired spin-state is a nonet: the state with component of spin MS = 4 and spin S = 4. In order to define this type of calculation other keywords must also be used. For a 'simple' nonet calculation, use C.I.=8.
When the configuration interaction calculation is done, all microstates having a component of spin, MS, equal to 4 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 4, can be constructed. From this set, only a nonet state can be selected, all other states will be ignored. If ROOT=n is present, then the n'th nonet state will be selected, otherwise the first nonet state will be chosen.
The nonet states are the highest spin states normally calculable using MOPAC in its unmodified form. If several nonets are to be calculated, say the second or third, then C.I.(n1,n2) should be used.
See also SINGLET, DOUBLET, TRIPLET, QUARTET, QUINTET, SEXTET, SEPTET, and OCTET.
UHF interpretation: The system will have eight more alpha electrons than beta electrons.