Extension of the multiconfiguration Hartree-Fock method to allow double photoionization of atoms

Very recently we were successful in extending the multiconfiguration Hartree-Fock (MCHF) method for electron-impact ionization of atoms to allow double photoionization of atoms. We report, as a test case, the results of our calculation of the triple differential cross section (TDCS) for double photoionization of helium. We have calculated the initial state in the Hartree-Fock and the MCHF approximations and the final state in the Coulomb approximation and the screening potential approximation in order to compare with previously published works. We compare the present results calculated at 30-eV excess photon energy shared equally by two final-state continuum electrons, with other similar theoretical calculations. Finally, we also calculate the TDCS at 20-eV excess photon energy to compare with experimental observation