3. Summary

In summary, our results demonstrate that at all energies atomic photoionization can be characterized in terms of a very limited number of measurable atomic parameters associated with independent particle approximation matrix elements. At high energy only Coulomb matrix elements are needed, while at lower energies one must include low multipole screening contributions, but never higher than octupole, in order to make predictions accurate within $1\%$. Quadrupole screening can be important except in the lightest elements. Octupole screening can be important in inner shells of intermediate Z atoms and in all shells of high-Z atoms. These results should be relevant to experimental measurements of nondipole effects in photoionization angular distributions [8].