Positronium formation for e+-Na scattering at low and intermediate energies

There have been various theoretical calculations for positron-sodium scattering that attempt to calculate accurate positronium(Ps) formation cross sections at low and intermediate energies. The recent hyperspherical close-coupling (HSCC) calculations (Le et al. 2005 Phys. Rev. A 71, 032713) has handled the contribution from the positronic bound states to a great extent. Their calculations have further strengthened the argument that the theoretical Ps cross sections at low energies deviate from the predictions of the experimental measurements (Surdutovich et al. 2002 Phys. Rev. A 65, 032713). Here we examine whether the inclusion or the neglect of the positronic bound states in the calculation have any significant effects on the low energy Ps formation cross sections. Thus, we attempt to investigate if large-scale CC calculations are deficient in this respect.