Anisotropy Not all particles are well approximated as spheres. In the analysis of Fig. , we smoothed over anisotropy by considering the mean polarizability over the three principal axes. One way to capture the influence of non-sphericity is to fit an ellipsoidal model. As discussed in Sec. 2.6, defining the volume of a particle is nontrivial. Moreover, a Bader volume cannot be calculated for a particle in vacuum. One way to proceed is to consider a bounding box that encloses the electron delocalization volume of the inclusion.