Following the computational protocol developed in our previous works , we assessed the degree of spin-density delocalization by employing the Becke population analysis (for comparison of Becke, Mulliken, and Bader population analyses, see the Supporting Information [SI] for Ref. ). To this end, fine atom-centered Becke grids were generated with the Serenity program and used for spin-density integration over predefined atomic basins. This procedure ensures the error of numerical integration to be below about 5.0×10 -4 atomic units (a.u.). The ratios reported in this work and used as a measure of the spin-density delocalization are computed by summing up the Becke atomic populations over all atoms in a molecule. percentages of exact exchange below 50% predict most of spin density to be localized on the His molecule. This does not agree with experimental results , where about 82% of the spin density was found at Chl a. Increasing the amount of exact exchange to 50% with BHandHLYP, the spin density can be localized more on the Chl a molecule, whereas completely localized distributions can be found in case of the M06-HF functional (100% of exact exchange). In turn, however, increasingly large areas of negative spin density and larger spin contaminations are observed . The latter usually indicates a poor quality of the unrestricted DFT solution. It is interesting to note that calculations for the tilted structures do not show a noticeable change in the internal Chl a spin-density distribution nor in its intermolecular delocalization degree. Therefore, KS-DFT calculations are apparently inconclusive and unable to provide useful insight into the spin-density distribution of the hinge model. As was already discussed above, this behavior of the KS-DFT method is not surprising and is related to the SIE , which often leads to overdelocalized spin densities . ergetic ordering of MOs . Alternatively, one can argue that the accuracy of FDE-diab is not sufficiently high to correctly reproduce such small energy differences. In fact, this could also be problematic with the standard KS-DFT approach (e.g., see calculations for Mg-porphyrin and Mg-chlorin electronic states in Ref. ).