Modeling the electronic structures of the ground and excited states of the ytterbium atom and the ytterbium dimer: A modern quantum chemistry perspective

We present a comprehensive theoretical study of the electronic structures of the Yb atom and the Yb2 molecule, respectively, focusing on their ground and lowest‐lying electronically excited states. Our study includes various state‐of‐the‐art quantum chemistry methods such as CCSD, CCSD(T), CASPT2 (including spin‐orbit coupling), and EOM‐CCSD as well as some recently developed pCCD‐based approaches and their extensions to target excited states. Specifically, we scan the lowest‐lying potential energy surfaces of the Yb2 dimer and provide a reliable benchmark set of spectroscopic parameters including optimal bond lengths, vibrational frequencies, potential energy depths, and adiabatic excitation energies. Our in‐depth analysis unravels the complex nature of the electronic spectrum of Yb2, which is difficult to model accurately by any conventional quantum chemistry method. Finally, we scrutinize the bi‐excited character of the first 1Σg+ excited state and its evolution along the potential energy surface. Atomic and molecular ytterbium are of central importance in modern physics. Yet, the physical interpretation and further analysis of their properties has to be often based on reliable quantum chemical calculations. This work reports a thorough theoretical study of the electronic structures of atomic and molecular ytterbium using both state‐of‐the‐art and unconventional electronic structure methods.