Time-dependent coupled-channel calculation for elastic scattering of positrons by hydrogen atoms and helium ions

We investigate elastic scattering of positrons by hydrogen atoms and helium ions using a time-dependent coupled-channel (TDCC) method. Phase shifts are calculated with the time-energy Fourier transform of a wave packet. Numerical accuracy of the TDCC method is demonstrated for S-, P-, and D-wave scatterings by hydrogen atoms. For helium ions, we examine the low-lying S-wave resonances with a broad width recently predicted in variational eigenenergy calculations. However, resonancelike behaviors are not discernible in the S-wave phase shift for the ground-state target.