Modeling positronium beyond the single particle approximation

Abstract

Understanding the properties of the positronium atom in matter is of interest for the interpretation of positron annihilation experiments. This technique has a unique capability for the investigation of nanometer sized voids and pores soft molecular materials (polymers, liquids or biostructures) and porous materials. However, detailed interpretations of the experimental data rely on modeling of the annihilation properties of positronium in the host material. New applications of the technique are being developed but the computational models still are based on single particle approaches and there is no way to address the influence of the electronic properties of the host material. In this work we discuss new directions of research.

Pore Topology Effects in Positron Annihilation Spectroscopy of Zeolites

“…A more accurate description of Ps requires considering the non‐adiabatic electron‐positron correlation effects, but it is still an open problem which will require new modeling approaches and more computing power . Note that although for simplicity purely siliceous frameworks have been considered, with appropriate parameterization the model could be extended to introduce other heteroatoms (e.g.…”

B-spline basis implementation of the Hartree-Fock method for arbitrary central potentials

“…Here the first term in the bracket is the kinetic energy operator, and the second term is a local central potential V (r). For an atom with atomic number Z, V (r) = −Z/r, but in the BSHF program [10] it can also be chosen to be an arbitrary central potential, e.g., a harmonic confining potential, for a system of electrons to approximate the electron gas in the background of a uniform positive-charge distribution [17]. The Hartree-Fock potentialV HF = N i=1 Ĵ i −K i is a sum of the direct and (non-local) exchange terms J i φ j (x) = dx i φ * i (x )ρ −1 φ i (x )φ j (x) andK i φ j (x) = dx i φ * i (x )ρ −1 φ j (x )φ i (x), where ρ = |r − r|.…”

Positron surface state as a spectroscopic probe for characterizing surfaces of topological insulator materials

“…In systems where the spin cannot be considered a good quantum number, however, a more careful examination is required. In general, we can write the momentum density of the annihilating electronpositron pairs as 24,25 :…”