Since the pronounced electric field patterns described above are robust, and are not the result of a couple of specific residues, but are caused by a collection of them, one can speculate that they may not have arisen by accident but may have emerged over the course of evolution. For comparison, the electrostatic environment around another pair of Fe sites, Fe4 and Fe5, is displayed in Figure (plots comparing the OLEFs around all pairs of Fe sites, as well as the Mo site, can be found in Section S4 of the Supporting Information). Note that this pair has previously been considered as plausible alternative absorption sites for N2 in the computational work by Siegbahn and co-workers. Our electric field calculations indicate that no unequivocal electrostatic patterns are observable around these sites, regardless of the protonation state of His195; patches of field vectors of varying magnitude, pointing in both directions, and attenuating at different rates, can be found around both. Additionally, only faint field vectors, with magnitudes of the order of ±0.1 VÅ -1 , are observed along the Fe2-Fe6 axis.