Optical-Potential Calculation of Electron-Hydrogen Singlet Scattering

The use of the optical potential or self-energy of the single-particle Green's function for elastic electronatom scattering is discussed. The usual formalism, which assumes an unperturbed state described by a single determinant, is generalized to include unperturbed states described by a linear combination of determinants. Calculations are carried out for $S$-wave, elastic, singlet scattering of electrons by hydrogen atoms. The results are compared with the accurate variational calculations by Schwartz.