Calculation of Low-Energy Positron-Atom Scattering with Square-Integrable Wavefunctions

The variational method is applied to the low-energy positron scattering and annihilation problem. The ultimate aim of the investigation is to find a computationally economical way of accounting for strong electron-positron correlations, including the effect of virtual positronium formation. The method is applied to the study of elastic s-wave positron scattering from a hydrogen atom. A generalized eigenvalue problem is set up and solved to obtain s-wave positron-hydrogen scattering phase shifts within 8x10(-3) rad of accepted values. This is achieved using a small number of terms in the variational wavefunction; in particular, only nine terms that depend on the electron-positron distance are included. The annihilation parameter Z(eff) is also calculated and is found to be in good agreement with benchmark calculations.