Many-body theory of positron-molecule interactions

Calculations are performed for positron binding to molecules, Doppler-broadened γ-spectra for positron annihilation on molecules, and positronic bonding in systems of dianions. Implemented in the state-of-the-art massively parallelized C++ code EXCITON+ [J. Hofierka et al. Nature 606 688 (2022)], the approach uses the Feynman diagram technique to construct a positron-molecule self-energy that accurately accounts for important electron-positron correlations including polarization of the target by the positron, screening of the Coulomb interaction, electron-hole interactions, virtual positronium formation and positron-hole interactions. <br><br>Chapters 3 and 4 present positron binding energy calculations for halogenated hydrocarbons and heterocyclic ring molecules respectively.

Very good agreement with experiment is found (to within 1 meV in cases), especially for the ringed molecules where blind comparisons with experiment are made. For halogenated hydrocarbons, the general effect of halogenation on the binding energies is quantified and explained. For the ringed molecules, the interplay between permanent dipole moments and molecular π-bonds in determining the localization and shape of the correlated positron Dyson wavefunction is highlighted.<br><br>Chapter 5 extends the present MBT to the calculation of Doppler-broadened γ-spectra.