It is shown that the Fredholm determinant for the Lippmann-Schwinger equation may be computed for complex energies using only $L^2$ basis functions. Analytic continuation to the real axis in the $E+i\epsilon$ limit gives elastic scattering phase shifts over a continuous range of energies, showing that it is not necessary to explicitly enforce asymptotic boundary conditions for numerical scattering computations, and suggesting that elastic electron-atom or -ion scattering information may be obtained using standard bound-state configuration-interaction methods.

• Received 30 December 1971

DOI:https://doi.org/10.1103/PhysRevLett.28.401