ACCURATE LOCAL-DENSITY PHOTOIONIZATION CROSS-SECTIONS BY LCAO STIELTJES IMAGING APPROACH

Photoionization cross sections are evaluated at the local density level avoiding any potential shape approximation by employing the Stieltjes imaging (ST) technique in conjunction with large (STO) basis LCAO calculations. The ST technique proves accurate in comparison with full continuum calculation on the noble gases ionization. Several choices for the final-state potentials, including different exchange-correlation potentials, are tested on the noble gases, as well as in H2O and CO. Finally, several molecules are investigated employing the transition-state x alpha potential and the results compared with available experimental data and previous calculations. The accuracy of the proposed approach appears quite comparable to the ab initio static-exchange level, removing spurious resonances associated to the muffin-tin approximation, and should prove useful in the analysis and interpretation of cross-section data for large systems, where it is shown that basis-set requirements become less stringent. The accuracy obtainable for the cross-section profiles allows close comparison with experimental data, which, although showing good general agreement for the shape of the cross-section profile, indicates the need of a further refinement of the theoretical model. (C) 1995 John Wiley and Sons, Inc.