An important aspect of the MI indices is that the theory of quantum entanglement and correlation measures is built on the premises of mutually orthogonal Hilbert spaces. This is not satisfied by construction when working with traditional AOs, because of the non-zero overlaps between different AOs. For our purposes, it is essential to work with orbitals that are both localized and orthogonal. Many localization schemes exist in the literature for organic chemistry purposes , however, we will work here with the straightforward so-called symmetric orthogonalization, defined by c : jσ "