Reexamination of the ground-state Born-Oppenheimer ${\mathrm{Yb}}_2$ potential

The precision of the photoassociation spectroscopy of the Yb dimer in degenerate gases is enough to improve the constraints on short-range gravitylike forces if the theoretical knowledge of the Born-Oppenheimer interatomic potential and non-Born-Oppenheimer interactions is refined [Borkowski et al., Sci. Rep. 9, 14807 (2019)]. The ground-state interaction potential of the ytterbium dimer is investigated at the exact two-component core-correlated coupled-cluster method with singles, doubles, and noniterative triples [CCSD(T)] level of ab initio theory in the complete-basis-set limit with extensive augmentation by diffuse functions. For the small basis set the comparison is made with the four-component relativistic finite-nuclei CCSD(T) calculations to identify the contraction of the dimer bond length as the main unrecoverable consequence of the scalar-relativistic approximation. The empirical constraint on the number of bound vibrational energy levels of the ${}^{174}\mathrm{Yb}_2$ dimer is accounted for by representing the global ab initio–based Born-Oppenheimer potential with the model semianalytical function containing the scale and shift parameters. The results support the previous evaluation of the Yb dimer potentials from the photoassociation spectroscopy data and provide an accurate and flexible reference for future refinement of the constraints on short-range gravitylike forces by ultracold atomic spectroscopy.

Figure 1

Correlation of the scaled binding energy and shifted equilibrium distance of the ${\mathrm{Yb}}_2$ interaction potential based on the ab initio $\mathrm{V}n\mathrm{Zbf}$ c28 data. Solid lines represents the linear fit. The cross indicates the scaled Born-Oppenheimer result from Ref. [11].