The ground state potential of the beryllium dimer

An ab initio X (1) Sigma(g)(+) Be-2 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 R(e) = 4.627 bohr in full agreement with experiment and the dissociation energy is obtained to D-e = 4.058 mE(h) (893 cm(-1)), significantly larger than the experimental estimate of D-e = 790 +/- 30 cm(-1). Delta G(1/2) 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 P-3 atoms.