Polarization effects, shape resonances and bound states in low energy positron elastic scattering by Zinc and Cadmium vapours

Abstract

Low energy elastic positron scattering from Zn and Cd atoms was studied using model correlation potential. Special attention is given to the study of polarization effects through the incorporation of quadrupole polarizabilities and hyperpolarizabilities in the scattering potential. Resonant p-wave shape structures are found for both systems. Results show that these become sharper and move to lower energies as the level of polarization of the potential is increased. Resonance was suppressed in Cd when the second hyperpolarizability γ was taken greater than 46000 a.u. and true p-wave bound states were formed. Comparison to previous calculations and dependence of the results with the scheme adopted to match the correlation and polarization components of the potential is discussed. We find that the elastic cross sections and the resonant effects do not depend on the specific form of the correlation potential but strongly depend on the polarization parameters and the matching point determined by the crossing between the correlation and polarization components of the potential. The value for the dipole–dipole–quadrupole polarizability B for Cd was specifically calculated using the relativistic coupled-cluster approach and is reported for the first time in this work.