Signature of chaos in high-lying doubly-excited two-electron atoms

Recently proposed diabatization and truncation techniques are used in solving Schr\"{o}dinger equation for two-electron systems. Within this method, it is easy to obtain relatively high accurate energy levels for doubly-excited states of a given symmetry. Nearest-neighbor spacings (NNS) statistics of the energy levels are performed for real 3D helium atom below ionization threshold $I_{20}$. The ss model of helium-like ions are also used, which allows us to analyze NNS up to $I_{35}$. We show evidence of the transition towards Wigner distribution as the energy range gets closer to double-ionization threshold.