Positron-atom scattering using pseudo-state energy shifts*

A simple way to generate low-energy phase shifts for elastic scattering using bound-state calculations is applied to the problem of $e^+$-Mg and $e^+$-Zn scattering. The method uses the energy shift between a small reference calculation and the largest possible configuration interaction calculation of the lowest energy pseudo-state/s as the input to tune a semi-empirical optical potential. The $s$- and $p$-wave phase shifts up to the first excitation threshold are given for both systems. The $e^+$-Mg cross section has a prominent $p$-wave shape resonance at an energy of about 0.0094 eV with a width of 0.0108 eV. The cross section maxima is about 4800 $a_0^3$, while the $Z_{\rm eff}$ achieves a value of 1300 at an energy of 0.108 eV.