Many-body theory calculations of positron binding to parabenzoquinone

Positron binding in parabenzoquinone is studied using $\mathit{\text{ab}}\mathit{\text{initio}}$ many-body theory. The effects of electron-positron correlations including polarization, virtual positronium formation and positron-hole repulsion, as well as those of $\pi$ bonds, aromaticity, and lone electron pairs, are considered. The binding energy is calculated as 60$\pm$16 meV, considerably larger than the 0.0925 meV value inferred from recent scattering calculations of [G. Moreira and M. Bettega, {\emph{Eur.~Phys.~J.~D}} {\bf 78} (2024)], but substantially smaller than we find in benzene (148$\pm$26 meV). The positron contact density (lifetime) is calculated as 8.0$\times {10}^{-3}$ a.u. (2.48 ns), vs.~1.61$\times {10}^{-2}$ a.u. (0.81 ns) in benzene. The decrease (increase) in binding (annihilation rate) in parabenzoquinone compared to benzene is ascribed to the loss of aromaticity: the electron density on the positive oxygen nuclei being relatively harder for the positron to probe compared to the aromatic rings in benzene.