quantifies the degree of correlation (that has both quantum and classical origin) between the orbitals i and j as they are embedded in the whole system. Here, it is noteworthy to emphasize the key distinction between sp2q ij and I ij . sp2q ij computes the entanglement between the orbital pair i and j with all other active-space orbitals (the environment) while I ij quantifies only the specific correlation between orbitals i and j, within the environment. This allows for a more targeted analysis of the direct correlation between these two orbitals, see Figure . It is good to keep in mind that the definition of mutual information can be conceptually extended beyond the single spin-orbital level. For instance, we will discuss the mutual information between blocks of several spin-orbitals, typically associated with atoms, which we will refer to as I pbq AB , or the mutual information between block-A and block-B.