Numerical multiconfiguration Hartree-Fock studies of atomic photoionization cross sections: Dynamical core-polarization effects in atomic sodium

Completely numerical multiconfiguration Hartree-Fock (MCHF) methods are used to calculate the photoionization cross section of atomic sodium in its ground state for incident photon energies in the single-channel region between the first (3s/sup -1/)1S and second (2p/sup -1/)3P ionization thresholds. Particular attention is focused on obtaining accurate cross-sectional values in the threshold and Cooper-minimum region up to ∼5 eV kinetic energy, where there is the possibility of a sensitivity of results to the quality of the ground-state wave function and final-state potential, and on incorporating the effects of dynamical core polarization in the final state, which are particularly important in the ∼5--15-eV kinetic energy region. These attributes are incorporated in the MCHF procedure by including appropriate doubly excited configurations in the ground state and L2 polarization pseudostates in the final-state wave function. Provision is made in the final-state calculation for the simultaneous variational determination of the continuum function, of the orbitals comprising a basis for the L2 polarization pseudostates, and of the configuration-mixing coefficients at each photon energy. The cross sections calculated in this way using length and velocity forms are in good agreement over the entire incident photon energy range considered, suggesting that converged values may be obtained in this interval from the present development. The very small effects of spin-orbit interaction on the photoionization cross section are neglected in the present calculations, in accordance with previously reported observations