Box-based convergent close-coupling method for solving Coulomb few-body problems

We present an implementation of the convergent close-coupling (CCC) method, in which the Laguerre-based target states are replaced with box-based eigenstates. Discrete energies are obtained by taking the states that vanish at the box radius R0, with convergence being established by simply varying R0. Excellent agreement between box- and Laguerre-based CCC, exterior complex scaling, and renormalized experiment is obtained for one of the most difficult three-body Coulomb breakup problems, near-threshold electron-impact ionization of atomic hydrogen. The simplicity of the box-based CCC method is expected to lead to a greater understanding of the close-coupling formalism generally.