We note that finding the correct effective volume for finite systems is not trivial, and that if the effective volume stays the same for the molecules in the two electronic states. This implies that, for instance, in x-ray diffuse scattering studies the volume-based error should cancel out in the calculated x-ray difference-scattering signal from these RDFs. Besides from these observations, it also is evident from the figure that far from all of the differences in solvation structure can be explained by the effective-volume discrepancy alone. Especially the Fe-O RDF differences due to system size (magenta and black lines) are far smaller than the differences due to potential (red and magenta lines). Before continuing to investigate the interactions within the solvent shell themselves, we also show the effects on the solvent shell of the counterions in the system, by repeating the small-system simulation after removing the counterions (dashed magenta lines in figure ). Since the small system size gives a high effective concentration (roughly 180 mM, or ∼ 18 times higher than what is used experimentally ), it forces the counterions closer to the complex. Thus, they may affect the structure of its solvent shell. Comparing the solid and dashed magenta lines, we observe that simulations including the counterion produces a C-O RDF with an considerably larger first peak, which has also shifted towards shorter C-O distances, compared to the simulation without the counterions. This indicates that the (necessary) presence of the counterions can indeed affect the shell structure. In this case, the presence of counterions in the vicinity of the complex seem to increase the C-O coordination, because the waters are actually coordinated to Cl -, which are now only kept at a fixed distance of roughly 7.5 Å from the Fe atom, due to the smaller box size.