Ab initio Potential Energy Curve for the Ground State of Beryllium Dimer

This work concerns ab initio calculations of the complete potential energy curve and spectroscopic constants for the ground state X¹Σ_g⁺ of the beryllium dimer, Be₂. High accuracy and reliability of the results is one of the primary goals of the paper. To this end, we apply large basis sets of Slater-type orbitals combined with high-level electronic structure methods including triple and quadruple excitations. The effects of the relativity are also fully accounted for in the theoretical description. For the first time the leading-order quantum electrodynamics effects are fully incorporated for a many-electron molecule. Influence of the finite nuclear mass corrections (post-Born–Oppenheimer effects) turns out to be completely negligible for this system. The predicted well-depth (D_e = 934.6 ± 2.5 cm^–1) and the dissociation energy (D₀ = 807.7 cm^–1) are in a very good agreement with the most recent experimental data. We confirm the existence of the weakly bound twelfth vibrational level [Patkowski et al. Science 2009, 326, 1382] that it lies just below the onset of the continuum.