Double K-shell photoionization of atomic beryllium

Double photoionization of the core 1s electrons in atomic beryllium is theoretically studied using a hybrid approach that combines orbital and grid-based representations of the Hamiltonian. The 1 S ground state and 1 P final state contain a double occupancy of the 2s valence shell in all configurations used to represent the correlated wave function. Triply differential cross sections are evaluated, with particular attention focused on a comparison of the effects of scattering the ejected electrons through the spherically symmetric valence shell with similar cross sections for helium, representing a purely two-electron target with an analogous initial-state configuration.