# Molecular size effects on diffraction resonances in positronium formation from fullerenes

## TL;DR

This study investigates how increasing the size of fullerenes from C60 to C240 affects diffraction resonances in positronium formation, revealing that larger fullerenes cause these resonances to become more compact in energy, which has implications for spectroscopic experiments.

## Contribution

The paper extends previous work by analyzing larger fullerenes, demonstrating the energy compactification of diffraction resonances in positronium formation, and models the fullerenes using a spherical jellium approach with LDA.

## Key findings

- Diffraction resonances become more compact with larger fullerenes.
- Resonance behavior is analogous to classical slit diffraction.
- Results support further positronium spectroscopic experiments.

## Abstract

We previously predicted [P.A. Hervieux et al., Phys. Rev. A \textbf{95}, 020701 (2017)] that owing to predominant electron capture by incoming positrons from the molecular shell, C$_{60}$ acts like a spherical diffractor inducing resonances in the positronium (Ps) formation as a function of the positron impact energy. By extending the study for a larger C$_{240}$ fullerene target, we now demonstrate that the diffraction resonances compactify in energy in analogy with the shrinking fringe separation for larger slit size in classical single-slit experiment. The result brings further impetus for conducting Ps spectroscopic experiments with fullerene targets, including target- and/or captured-level differential measurements. The ground states of the fullerenes are modeled in a spherical jellium frame of the local density approximation (LDA) method with the exchange-correlation functional based on the van Leeuween and Baerends (LB94) model potential, while the positron impact and Ps formation are treated in the continuum distorted-wave final state (CDW-FS) approximation.