Model-potential calculations of positron binding, scattering, and annihilation for atoms and small molecules, using a Gaussian basis

A. R. Swann; G. F. Gribakin

doi:10.1103/PhysRevA.101.022702

paper

Model-potential calculations of positron binding, scattering, and annihilation for atoms and small molecules, using a Gaussian basis

arXiv:1912.03051 · doi:10.1103/PhysRevA.101.022702

Abstract

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, H $_{2}$ , N $_{2}$ , Cl $_{2}$ , and CH $_{4}$ . 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 $Z_{eff}$ from discrete positive-energy pseudostates. Good agreement between the present results and existing calculations and experimental data, where available, is obtained, including the $Z_{eff}$ value for CH $_{4}$ , which is strongly enhanced by a low-lying virtual positron state. An exception is the room-temperature value of $Z_{eff}$ for Cl $_{2}$ , 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 Cl $_{2}$ might support a bound state for the positron, with a binding energy of a few meV.

23 pages, 10 figures, accepted in Phys. Rev. A

Model-potential calculations of positron binding, scattering, and annihilation for atoms and small molecules, using a Gaussian basis

Abstract

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