As the nuclear charge Z is continuously decreased an N-electron atom undergoes a binding-unbinding transition. We investigate whether the electrons remain bound and whether the radius of the system stays finite as the critical value Zc is approached. Existence of a ground state at Zc is shown under the condition Zc < N - K, where K is the maximal number of electrons that can be removed at Zc without changing the energy.
Boundary Conditions Effects on the Ground State of a Two-Electron Atom in a Vacuum Cavity
