Method to compute atomic and molecular photoionization cross sections by use of basis sets.

Abstract

An alternative approach is presented to the problem of computing atomic and molecular photoionization cross sections by use of basis sets. The present method is based on a simple integral equation that relates the real polarizability on the imaginary frequency axis to the photoionization cross section. Hence the computational work consists in obtaining polarizabilities for imaginary frequencies. Many-body perturbation theory is used for that purpose, and the perturbation expansion is complete to second order in the Coulomb interaction. In that way there is a comprehensive inclusion of correlation effects. Techniques to invert the integral equation to obtain photoionization cross sections from the computed polarizabilities are discussed, and results are given for the atomic systems neon and argon as test cases.