Perturbation Corrections to the Uncoupled Hartree–Fock Method. Dipole Polarizabilities of the Neon Isoelectronic Sequence

The polarizability, α = α0 + α1, for the 10-electron atomic systems Ne, Na+, Mg2+, Al3+, and Si4+ has been calculated by the uncoupled Hartree–Fock method with the perturbation correction of Tuan and co-workers (PUCHF Method). The correction is rather significant, with the percentage ratio α1 / α% being around 20%. The contributions to α from individual orbitals were also investigated. It is shown that the outermost orbitals and the orbitals along the direction of external electric field give the largest contribution to α: The contribution from the two 2p0 orbitals is around 31.1%–42.2%. The α obtained by the PUCHF method differs from the coupled Hartree–Fock (CHF) method by 3.6% to 4.8% except for the neutral atom Ne which differs by 7.8%. The agreement of α between the PUCHF and CHF methods improves with increase of nuclear charge, as has been observed previously for the dipole and quadrupole polarizabilities of He, Li, and Be isoelectronic sequences by Epstein and Johnson. It is concluded that (1) the PUCHF method offers a simple and tractable way to study the contribution of individual orbitals to physical properties, and (2) for polarizabilities of positive ions the PUCHF method gives results with accuracy comparable to those obtained from the CHF method.