Complexity function of jammed configurations of Rydberg atoms

In the preceding chapters, we have concentrated on atomic ground configurations and ground states, as well as atomic states where just one electron is excited and where this excitation is not above, or close to, the ionisation limit. For the most part, we will leave the detailed studies of more complicated systems to other volumes. In this chapter, we just introduce a few extensions. We look at atoms with more than one electron excited. Such states tend to lie above the first ionisation limit, and hence they are often auto-ionising. That makes it natural to discuss them in concert with atomic states coupled to a continuum. However, there are some examples of truly bound doubly excited states, and we give one example. The chapter also introduces Rydberg atoms, for which one electron is excited to a very high principal quantum number, while still being in a bound state. Briefly, we cover atoms for which the excitation emanates from an inner shell, relevant for X-ray physics, and also highly ionised atoms.