The LASSCF method (originally introduced as cMF but independently re-derived by us as a generalization of density matrix embedding theory ) is an approximation to CASSCF in which the wave function is factorized as a single antisymmetrized product of subspaces which are localized in real space. This approximation itself is not qualitatively accurate for multimetallic compounds involving interactions among the metal centers, even if they are weak, for the simple reason that the spin operator ( Ŝ2 ) is nonlocal. However, LASSCF states can serve as an efficient model space for the localized active space state interaction (LASSI) method, which recovers correlation between the subspaces. LASSI achieves this by projecting the molecular Hamiltonian into a model space of LAS wave functions which share the same set of orbitals in each subspace but possess different quantum numbers (e.g., number of electrons, local spin, and excitation number).