Extraction of Scattering Information from Bound-State Configuration-Interaction Computations: Elastic Electron-Hydrogen Scattering

Using the fact that for complex energies the Fredholm determinant, D(z), for the partial wave Lippmann‐Schwinger equation may be constructed using only square integrable (L²) basis functions, electron‐hydrogen‐atom elastic phase shifts are computed using input generated from a standard bound‐state Hylleraas program. The necessary numerical analytic continuation needed to take the $\mathrm{z=E+i\epsilon }$ limit is performed by the pointwise rational‐fraction method and yields the phase shift over a continuous range of energies from a single major computational step. No integrals over non‐L² functions are needed for the computation.