The RAS2 space is the active space and should include the most important orbitals needed to describe the electronic states of interest; the m ∈ RAS2 in Eq. ( ) includes all configurations within the active space, meaning that RAS-SF resembles a CAS-CI method within the RAS2 space. The RAS1 space contains all doublyoccupied orbitals and RAS3 contains virtual orbitals, and we allow single excitations between these two subspaces and RAS2, corresponding to holes h ∈ RAS1 and particles p ∈ RAS3. This particular ansatz has been called RAS(h,p)-SF. To describe CT states, 11 the high-spin reference orbitals are first localized onto molecular fragments, where they are then categorized by subspace (RAS1, RAS2, or RAS3) and by fragment. The RAS Hamiltonian is then partitioned into CT and non-CT blocks, where the latter will also be called the "locally-excited" (LE) block. Diagonalization of these blocks provides either the LE states or the CT states, and the latter are further grouped into left-right versus right-left character, or equivalently A → B versus B → A (Fig. ).