A FCI benchmark on beryllium dimer: The lowest singlet and triplet states

The electronic structure of the beryllium dimer Be2 was investigated at valence Full-Configuration-Interaction (FCI) level, using a large cc-pV6Z basis set, (7s6p5d4f3g2h1i). This gives a total of 280 contracted Gaussian functions for the dimer, corresponding to a valence FCI space of about 185 × 10 6 symmetry-adapted Slater determinants. The adiabatic potential energy curves of the singlet ground X 1 Σ g + and the triplet lower excited ( 1 ) 3 Σ u + states were calculated, and the principal spectroscopic constants for the two states were evaluated. Our results are found to be very close to recent experimental values published in the literature.