The development of beams of fast bare ions in the last two decades has allowed atomic physicists to vary the coupling constant in non-trivial, ion-atom reactions and much has been learned. In real atoms the electrons provide a wide range of velocity scales. Thus, it becomes important to develop the theoretical and computational tools to describe excitation, ionization and charge transfer over broad energy regimes. The present work is based on a variational expansion of the scattering wavefunction in a truncated Hilbert space. The method goes beyond the independent particle model to describe an ion perturbing a fully correlated, two electron atom and given an interpretation of two electron pseudostates, allows a complete description of such systems. The eventual goal is to explore reacting, relativistic many-body systems.
