Figure 4.8. Effect of adding an additional energy of e2/(2R) to the calculated IP's from the model. Both experimental () and calculated () photoionization potentials are shown. This term represents the work required to remove an electron from a positive charge enclosed in a metal sphere of radius R. It corrects the global trend in the theoretical results so that they closely imitate the experimental results although with a constant error of about 1.5eV. For all but the smallest n<7 clusters the model is successful in explaining the observed behavior.