The basis set convergence of the Hartree–Fock energy for H2

By using completely optimized basis functions, it is shown that the Hartree–Fock energy for the H2 molecule converges exponentially, both with respect to the number of basis functions of a given type and with respect to the highest angular momentum functions included. With a basis set including up to h-functions, a subnanohartree accuracy can be obtained. These results clearly suggest that estimation of the complete basis-set limit should employ different extrapolation schemes for the Hartree–Fock and correlation energies.