Many-body theory of positron interactions with molecules

Abstract

This work develops a many-body theory of positron–molecule interactions and its implementation in our state-of-the-art parallelised open-source C/C++ program EXCITON+.
Calculations of positron binding, elastic scattering, and direct annihilation in polyatomic molecules are presented. The strong positron-molecule correlations are accounted for via a diagrammatic description of the self-energy of the positron in the field of the molecule.

It is constructed by solving the Bethe-Salpeter equations for the two-body propagators in the positron-electron, positron-hole, and electron-hole channels. Positron binding to negative ions, atoms, and molecules in the fixed-nuclei approximation is studied. For positron binding to molecules, the approach [published in J. Hofierka, B. Cunningham, C. M. Rawlins, C. H. Patterson and D. G. Green, Nature 606, 688 (2022)]: (i) gives the first ab initio calculations in close agreement with data from over two decades of pioneering experiments; (ii) provides fundamental insight into the role of correlations including quantifying the role of virtual-positronium formation in enhancing binding in polar molecules and enabling binding in non-polars, and increasing annihilation rates by 2 to 3 orders of magnitude; and (iii) proposes a computationally less expensive approach to account for the important process of virtual-positronium formation, demonstrated by predicting binding energies in DNA nucleobases.

Date of Award	Jul 2024
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	European Research Council
Supervisor	Dermot Green (Supervisor) & Myrta Grüning (Supervisor)