The ground state potential of the beryllium dimer

An ab initio X1Σg+Be2 ground state potential is determined from all-electron SCF/valence-shell MR-CI calculations which account for core-valence correlation by an effective core polarization potential. The position of the minimum is found at Re=4.627 bohr in full agreement with experiment and the dissociation energy is obtained to De=4.068 mEh (893 cm−1, significantly larger than the experimental estimate of De=790 ± 30 cm−1. ΔG12 is calculated from an analytical form of the potential to be 218.4 cm−1, in slight variance with the observed value of 223.8 cm−1. Discrepancies below 10 cm−1 remain with the observed (less accurate) higher vibrational spacings. The deep inner minimum is shown to be related to chemical binding from interaction with a promoted configuration of spin-paired 3P atoms.