The beryllium dimer potential

The convergence of ab initio calculations of the beryllium dimer potential is examined with several basis sets orders of perturbation theory. When the atomic pair natural orbital basis set calculations are extrapolated to the complete basis set and full CI limits, the calculated parameters: R_e=2.447 Å, D_e=827 cm^?1, ν₀₁=212.7 cm^?1, ν₁₂=167.2 cm^?1, ν₂₃=121.5 cm^?1 and ν₃₄=77.7 cm^?1 are in good agreement with the experimental parameters: R_e=2.45 Å, D_e=839±10 cm^?1, ν₀₁=223.2 cm^?1, ν₁₂=169.7 cm^?1, ν₂₃=122.5 cm^?1, and ν₃₄=79 cm^?1.