Shortcomings of the R-matrix method for treating dielectronic recombination

By performing radiation-damped R-matrix scattering calculations for the photorecombination of Fe forming Fe, we demonstrate and discuss the difficulties and fundamental inaccuracies associated with the R-matrix method for treating dielectronic recombination ~DR!. Our R-matrix results significantly improve upon earlier R-matrix results for this ion. However, we show theoretically that all R-matrix methods are unable to account accurately for the phenomenon of radiative decay followed by autoionization. For Fe, we demonstrate numerically that this results in an overestimate of the DR cross section at the series limit, which tends to our analytically predicted amount of 40%. We further comment on the need for fine resonance resolution and the inclusion of radiation damping effects. Overall, slightly better agreement with experiment is still found with the results of perturbative calculations, which are computationally more efficient than R-matrix calculations by more than two orders of magnitude.