Pseudopotential study of the ground and excited states of Yb-2

The ground state of the van der Waals-type lanthanide dimer Yb-2 has been s tudied by means of relativistic energy-consistent ab initio pseudopotential s using three different core definitions. Electron correlation was treated by coupled-cluster theory, whereby core-valence correlation effects have be en accounted for either explicitly by correlating the energetically highest coreorbitals or implicitly by means of an effective core-polarization pote ntial. Results for the first and second atomic ionization potentials, the a tomic dipole polarizability, and the spectroscopic constants of the molecul ar ground state are reported. Low-lying excited states have been investigat ed with spin-orbit configuration interaction calculations. It. is also demo nstrated for the whole lanthanide series that correlation effects due to th e atomic-like, possibly open 4f-shell in lanthanides can be modeled effecti vely by adding a core-polarization potential to pseudopotentials attributin g the 4f-shell to the core.