Taken together, the observations made above underscore that the negative field direction at Fe2 is not solely caused by the nature/orientation of His195 (and/or a couple of other key residues). Instead, it is a persistent effect induced collectively by multiple residues in coordination shells further away from the FeMoco. Note also that when a cluster model is applied to the modelling of nitrogenase activity -a popular choice to reduce the computational cost and enable the application of more accurate electronic structure methods -this mediumto long-range contribution to the OLEF is inevitably neglected, as even the most expansive clusters found in the literature do not include any residues beyond His195. To underscore the importance of this point, we computed how the electric field evolves as one removes residues in a gradually increasing radius around the FeMoco from the electric field calculation; almost 100 residues need to be removed for all the OLEFs to drop to values below ±0.1 VÅ -1 (when computing the electrostatics starting from the polarizable force-field, the number of residues that need to be removed to this end increases even further, to 112, cf.