LASSI[r,q] optimizes the CI vectors of these fragment statelets by solving Eq. ( ), which here corresponds to ϵ n given by Eq. ( ); and only incorporates the couplings, V 0n given by Eq. ( ), in the final construction and diagonalization of the model-space Hamiltonian matrix. The results for this molecule suggest that this procedure is fundamentally defective when applied to antiferromagnetic interactions between locally high-spin systems. For instance, in the simplest possible model space, consisting of only the two model states given by the bra and the ket of Eq. ( ), with the energy of the former expressed by E 0 , the diagonalization of the LASSI model-space Hamiltonian matrix would be expressed as the