Finite-size scaling method for the stability of atomic and molecular ions

Phase transitions at absolute zero temperature can take place as some parameter in the Hamiltonian of the system is varied. For the Hamiltonian of N-electron atoms, this parameter is taken to be the nuclear charge. As the nuclear charge reaches a critical point, the quantum ground state changes its characters from being bound to being degenerate or absorbed by a continuum. We describe the large-dimension approximation and the finite-size scaling method to calculate the critical nuclear charge for which an atom can bind an extra electron to form a stable negative ion. Results show that, at most, only one electron can be added to a free atom in the gas phase. The existence of doubly charged atomic negative ions in a strong magnetic field will be discussed