For the homogeneous PNP1 system (Fig. ), it can be seen that the largest errors are at the outer boundary, as one would expect. The relative absolute errors range between about 60-100 % at the outer boundary and diminish quickly toward the center of the simulation box. Indeed, the MAE in the induced dipoles in the outer part of the simulation box is 0.10 D and only 0.02 D in the inner part. This corresponds to MAPEs of 75 % and 7 % for the outer and inner parts, respectively. This behavior can be rationalized by the fact that water, while polar, is not very polarizable.