Figure 4.11. Ellipsoidal distortions shown as increases in axis size for each of the three dimensions. Plotted is d versus N where axes have length R=d +R0, with R0 the radius of the spherical cluster and N the number of atoms. The three symbol types (,,) represent the three axes – x,y,z. The assignment of x,y, and z is arbitrary. In the range 2—8 the transition spherical-prolate-distorted-oblate-spherical occurs as expected for a p-orbital. Other patterns are not so clear but the same trend is observed for the filling of each shell. 'Shape' isomers often exist near major transitions, e.g., Ag14 or Ag15. Note that rs is 3.02a0 for silver. These are the shapes with a high ionization potential that have been compared to the experimental results and not necessarily minimum energy shapes. This is why Ag19+ for example is spherical.