Basis-set convergence of the molecular electric dipole moment

摘要

The electric dipole moments (#mu#) of BH and HF are computed in conventional calculations employing different correlation-consistent basis sets at the levels of Hartree-Fock theory, second-order perturbation theory, and coupled cluster theory with single and double excitations, and single and double excitations with a perturbative triples correction. The basis-set convergence of #mu# is examined by comparison with results obtained with explicitly correlated wave function models. Inclusion of diffuse functions in the basis set is essential for accurate calculations of #mu#. They speed up the convergence at the Hartree-Fock level significantly and make the convergence at the correlated levels systematic. Once the outer valence regions important for #mu# are described accurately via the diffuse functions, the convergence at the correlated levels is governed by the interelectronic Coulomb singularity. For the aug-cc-pVXZ basis sets, the correlation contribution to #mu# follows #mu#_X~(corr) = #mu#_(lim)~(corr) + aX~(-3), which is similar to the form for the correlation energy, and extrapolated values based on this form represent a significant improvement on the ordinary basis-set results. Our estimates of the exact dipole moments #mu#_(e(HF)) = 1.8037 +- 0.0007D and #mu#_(0(BH)) = 1.3586 +- 0.0007D are in excellent agreement with the experimental values #mu#_(e(HF)) = 1.803 +- 0.002 D and #mu#_(0(BH)) = 1.27 +- 0.21 D.