Atomic correlation energies. I. Rigorous evaluation of E(2)for He, Li and Be

The authors have calculated the second-order perturbative corrections to the ground-state energy of He, Li and Be with the Hartree-Fock Hamiltonian as H 0 . Increasingly large basis sets were used, up to the point where results stabilised. The converged basis-independent second-order corrections are E he (2) =-0.0372 au, E Li (2) =-0.416 au and E Be (2) =-0.757 au, which amount to 88%, 92% and 80% respectively, of the experimental correlation energies.