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 X1Σg+ 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 (De = 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. Science2009, 326, 1382] that it lies just below the onset of the continuum.