Exact and Semiempirical Analysis of the Generalized-Random-Phase-Approximation Optical Potential

A many-body optical potential $\Sigma$ which has been demonstrated to give excellent electron-helium elastic scattering cross sections is analyzed. It is shown to encompass, yet be more general than, almost all previous model potentials used in electron scattering and Rydberg-state calculations. A partial semiempirical form of this potential is achieved. It is shown how $\Sigma$ can be computed by methods of variation-perturbation theory.