Note, the polarizabilities of the particles are less than those of analogous metallic spheres, which are represented by the gray line in the figure panel. In most cases, the particle volume was roughly spherical, becoming more spherical as the number of atoms increased. The change in electron density with the application of an electric field closely resembles the polarization charge induced on a sphere, or in a coarser approximation, the charge separation of a point dipole [Fig. ].