Dear All, I am currently working on an open-shell open-shell complex, which can exist as either a doublet or a quartet spin state, both of which contain three unpaired electrons. I am using a ROHF calculation which is then being used for orbitals for a RS2 calculation, with a restricted CAS. For the quartet, it is possible to obtain a good representation for the wavefunction, with the ROHF. However, for the doublet I cannot obtain a good initial guess at the wavefunction from the ROHF, as I cannot represent a doublet with three unpaired electrons. The RS2 does recover from the poor initial wavefunction, to a degree, giving three orbitals with single occupancy, but the resulting energies do not tally to the separate monomer calculations. Is there anyway of representing a doublet with three unpaired electrons, at the Hartree-Fock stage? Yours, Tony Starkey