Since the first protonation of 2 was found to be significantly uphill whereas protonation of 2 red occurred spontaneously, it is interesting to investigate at what stage reduction is most likely. However, reliable absolute reduction potentials are difficult to calculate, since they involve a change of the net charge, which gives rise to large and long-ranged Coulombic interactions that are difficult to describe accurately. We here follow a procedure developed for iron-sulfur clusters in proteins and use a correction term that was more recently proposed for Cu enzymes (see Computational Details). Since the reduction potentials have not been calibrated for LPMOs, we stress that the here reported values (see Table ) show trends rather than absolute values. Interestingly, we find that the lowest reduction potentials are obtained for the reduction of 2 HIE --→ 2 red HIE , which means that reduction at later stages of the reaction would be more favorable. It is interesting (although speculative) to compare the results in Table to the experimentally reported reduction potential (E • ) for the one-electron reduction of ascorbate (0.70 V-0.66 V) . This indicates that only the intermediate [Cu-OOH] 2+ with the second-coordination-sphere histidine protonated (3a HIP ) has a sufficiently high reduction potential to be reduced by ascorbate. Comparing with reductants such as CDH which have E • around 0.09 V-0.13 V is less informative but it still excludes reduction of 2 HIE . Thus, the most likely intermediate to be reduced is 3a HIP , which unfortunately is unlikely to form as described in the previous section. We therefore investigated a different possibility, namely that the first proton and electron transfer are coupled (PCET), particularly seeing that protonation of the superoxide in from HIP in 2 red HIP was spontaneous. To investigate PCET, we additionally calculated vertical electron attachment (VEA) energies for each step in the first proton transfer (see Fig. ). The VEA energy drops significantly at O d ...H ε2 distances greater than 1.8 Å, indicating that a PCET is indeed likely. We find that the VEA energy for the product is -216.0 kJ/mol. After optimizing the geometry (corresponding to 3j red ), the resulting intermediate is 36.8 kJ/mol lower in energy.