Inclusion of Positronium Formation Channels in Complex Optical Potential Models for Positron-rubidium Collisions

This paper presents a coherent quantum-scattering framework employing a multicomponent complex optical potential to model positron-rubidium (Z=37) collisions over the impact-energy range of 15 eV to 5000 eV. The target electronic structure is formulated using Clementi Roetti multi-zeta Roothaan Hartree-Fock-type orbitals, and the radial Schrödinger equation for continuum states is solved numerically by applying the Numerov scheme up to the truncation limit of lₘₐₓ=50. The quantitative analysis indicates a strong energy dependence in the DCS profile. At low impact energies(≤20eV), a fully coupled potential scheme captures a quantum interference minimum of 0.005 a.u. at an angle of 600 and a backward-scattering maximum of 0.03 a.u. at 1800 owing to core distortion. In the absence of virtual Ps exchange-correlation and non-local screening effects, there exist unphysical behaviour in which the DCS peak value at 00 increases from 0.04 a.u. to ~0.27 a.u. at 20 eV. Near the Ps formation threshold and at medium and higher incident electron energy (≥30eV),, competing inelastic processes, such as Ps generation, 5s valence excitation, and 4p inner shell ionization produce a volume absorption that strongly attenuates the elastic scattering, causing the DCS to become nearly flat above 400 down to a background level in the range 10-3 a.u. to 10-4 a.u. For higher energies (50eV to 100eV), the reduced time spent by the projectile in the target region makes the short-range correlations irrelevant, thus letting the imaginary part of the absorptive potential govern the process and resulting in confinement of the elastic flux into a very narrow forward cone(0⁰≤ θ ≤ {30}⁰), characterised by forward maxima increasing from ~ 2.2 a.u. for 50eV to more than 7.0 a.u. for 100 eV.