  The analytical treatment of the Greens function in the convergent
close-coupling method [Bray et al. Comp. Phys. Comm. 203 147 (2016)] has been
extended to charged targets. Furthermore, we show that this approach allows for
calculation of cross sections at zero channel energy. For neutral targets this
means the electron scattering length may be obtained from a single calculation
with zero incident energy. For charged targets the non-zero excitation cross
sections at thresholds can also be calculated by simply setting the incident
energy to the exact threshold value. These features are demonstrated by
considering electron scattering on H and He+.
