The three systems studied here: (a) copper reduction in water; (b) oxidation of [Cu(I)(NH3)4]+ in water; (c) copper reduction in a blue copper protein, plastocyanin. In (a–c), the minimal QM region is highlighted with a different representation compared to the solvent or the rest of the protein. In (c), 310 helices are colored violet, extended β sheet regions are colored orange, bridge β sheet regions are colored lime green, turns are colored ice-blue, and coils are colored pink. The figures are generated using VMD.39