An extension of the Kohn variational method for computing scattering amplitudes is demonstrated that requires only matrix elements of the resolvent of the Hamiltonian between energy-independent test functions. Scattering boundary conditions are imposed by expanding the resolvent in a basis of square-integrable functions and outgoing-wave continuum functions. By employing several continuum basis functions with overlaps defined by suitable analytic continuation, the scattering amplitude can be expressed efficiently over a continuous range of energies. The method described here differs from previous approaches using time-independent wave packets in that the wave packets which generate the initial and final states in this approach can lie within the interaction region. © 1998 The American Physical Society.
