IONIS: Approximate atomic photoionization intensities

A program to compute relative atomic photoionization cross sections is presented. The code applies the output of the multiconfiguration Dirac–Fock method for atoms in the single active electron scheme, by computing the overlap of the bound electron states in the initial and final states. The contribution from the single-particle ionization matrix elements is assumed to be the same for each final state. This method gives rather accurate relative ionization probabilities provided the single-electron ionization matrix elements do not depend strongly on energy in the region considered. The method is especially suited for open shell atoms where electronic correlation in the ionic states is large.Program summaryProgram title: IONISCatalogue identifier: AEKK_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEKK_v1_0.htmlProgram obtainable from: CPC Program Library, Queenʼs University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 1149No. of bytes in distributed program, including test data, etc.: 12 877Distribution format: tar.gzProgramming language: Fortran 95Computer: WorkstationsOperating system: GNU/Linux, UnixClassification: 2.2, 2.5Nature of problem: Photoionization intensities for atoms.Solution method: The code applies the output of the multiconfiguration Dirac–Fock codes Grasp92 [1] or Grasp2K [2], to compute approximate photoionization intensities. The intensity is computed within the one-electron transition approximation and by assuming that the sum of the single-particle ionization probabilities is the same for all final ionic states.Restrictions: The program gives nonzero intensities for those transitions where only one electron is removed from the initial configuration(s). Shake-type many-electron transitions are not computed. The ionized shell must be closed in the initial state.Running time: Few seconds for a large problem with a few thousand configurations.References:[1]F.A. Parpia, C.F. Fischer, I.P. Grant, Comput. Phys. Commun. 94 (1995) 249–271.[2]P. Jönsson, X. He, C.F. Fischer, I.P. Grant, Comput. Phys. Commun. 177 (2007) 597–622.

► Atomic photoionization often shows strong electron–electron interaction effects.
► This program computes photoionization in the relativistic multiconfiguration method.
► Electron–electron interaction in photoionization can be systematically studied.