Heavy atoms not only contain more electrons, they also possess inner shell electrons that are much more severely affected by relativity, quantum electrodynamics, and correlation. Present theoretical methods are based on the optimization of the total binding energy of all of the electrons, which is largely derived from portions of the wave function far from the nucleus. The short-range interactions are included only perturbatively, and thus these wave functions cannot be expected to precisely describe the atom in the region near the nucleus. One way to study the internal workings of a heavy neutral atom is to study highly ionized states of the same atom. If a theoretical model is to predict the global properties of a neutral lead atom, it should also predict the properties of a lead atom with 40 or 50 electrons stripped off.
Much work remains to be done in the determination of transition probabilities.
For multiply charged ions, the data consist almost exclusively of lifetime measurements, and virtually no branching ratio measure-ments have been made. Thus theoretical methods for the computation of branching ratios in complex ions are virtually untested. Electric polarizabilities of ground state ions are needed for the specification of long range interactions. Such cases provide very severe challenges to theoretical methods. Thus systematic and disciplined studies aimed at developing the means to comprehensively, accurately, and reliably quantifying atomic structure will be needed to meet the challenges of the next decade.