Asymptotic effective potentials for electron-hydrogen scattering

The asymptotic effective potential for electron- or positron-hydrogen elastic scattering is derived, correct to order x-7, using the Feshbach (Ann. Phys.; NY19:287 (1962)) optical potential as a starting point in the manner of Kleinman et al. (Phys. Rev.; 165:53 (1968)). To order x-6 the potential agrees with the close-coupling result of Seaton and Steenman-Clark (J. Phys. B.; 10: 2639 (1977)) but not to order x-7, where the present calculation gives the result +- 213/2x7 for electron and positron respectively. This coefficient differs considerably from the approximate value of Seaton and Steenman-Clark and the discrepancy is traced to the omission of d states in their calculation. (author)