The screening approximation for the helium sequence

Abstract Perturbation methods are employed to calculate a wide range of atomic parameters relating to the ground states of the helium iso-electronic sequence, the unperturbed eigenfunctions being products of screened hydrogenic orbitals. The screening constant enters as a dis­posable parameter. A means of choosing it is described which yields different values for different atomic properties. It is shown quantitatively that the simple calculations involved thereby lead to results of high accuracy.