Positron-atom scattering using pseudostate energy shifts

A method 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 after an initial validation on the e(+)-Cu system. The energy shift between a small reference calculation and the largest possible configuration interaction calculation of the lowest-energy pseudostate is used to tune a semiempirical optical potential. The potential was further fine-tuned by utilizing the energy of the second lowest pseudostate. The s- and p-wave phase shifts for positron scattering from Mg and Zn are given from threshold to the first excitation threshold. The e(+)-Mg cross section has a prominent p-wave shape resonance at an energy of about 0.096 eV with a width of 0.106 eV. The peak cross section for e(+)-Mg scattering is about 4800a(0)(2), while Z(eff) achieves a value of 1310 at an energy of 0.109 eV.