A model-potential method is employed to calculate binding, elastic scattering, and annihilation of positrons for a number of atoms and small nonpolar molecules, namely, Be, Mg, He, Ar, H2, N2, Cl2, and CH4. The model potential contains one free parameter for each type of atom within the target. Its values are chosen to reproduce existing ab initio positron-atom binding energies or scattering phase shifts. The calculations are performed using a Gaussian basis for the positron states, and we show how to obtain values of the scattering phase shifts and normalized annihilation rate Zeff from discrete positive-energy pseudostates. Good agreement between the present results and existing calculations and experimental data, where available, is obtained, including the Zeff value for CH4, which is strongly enhanced by a low-lying virtual positron state. An exception is the room- temperature value of Zeff for Cl2, for which the present value is much smaller than the experimental value obtained over 50 years ago. Our calculations predict that among the molecular targets studied, only Cl2 might support a bound state for the positron, with a binding energy of a few meV.
|Journal||Physical Review A (Atomic, Molecular, and Optical Physics)|
|Publication status||Published - 03 Feb 2020|