A modified adiabatic approach to positron-atom and positron-molecule polarisation potentials: application to positron-He scattering

A novel treatment of short-range correlation effects designed for use in calculating positron-atom and positron-molecule polarisation potentials is presented. The treatment is based on a physically motivated approximation that mimics the effect of the dominant non-adiabatic correction to the adiabatic potential at low scattering energies, namely virtual positronium formation. As an initial test of the method, positron-He scattering phaseshifts, scattering length and differential cross sections have been calculated and found to be in good agreement with accurate results. This method is immediately extendible to positron-molecule collisions and does not require significantly more work than a purely adiabatic treatment.