THE CONVERGENCE OF COUPLED-CLUSTER METHODS FOR BE2 - COMMENT

The convergence of coupled-cluster calculations of the beryllium dimer potential energy curve is examined. Different levels of coupled-cluster theory have been shown to give qualitatively different potential energy curves for Be2 when a 7s3p1d basis set is employed. However, the differences between the potential energy curves are much less dramatic in the complete-basis-set limit. Bartlett's recently reported coupled-cluster singles and doubles with fifth-order triples and quadruples, CCSD + TQ* (CCSD), method combined with extrapolation to the complete-basis-set limit results in good agreement with the experimental vibrational frequencies.