Abstract
An ab-initio calculation was performed to highlight the van der Waals interaction between Ba-0,Ba-+,Ba-2+ and helium atoms. The low-lying electronic states for Ba+He and BaHe systems have been determined with the ECP-CPP and full valence CI theory. However, the core-core interaction for Ba++He has been calculated by the CCSD(T). As a result, the spectroscopic parameters and the vibrational levels have been derived from Potential Energy Surface (PES) and compared with available theoretical and experimental data. Then, the permanent dipole moments for the ground and the excited states are determined. These results show an important shape in PES and allow checking the strong repulsive interactions between Rydberg electrons and the He atom. Furthermore, structures and stabilities of the Ba++Hen mixed-clusters have been investigated by exploring the PES based on the BHMC algorithm. The most stable icosahedral structure was detected at n = 12 and the snowball shell was completed at n = 20.