Science of materials opened up by positrons (Part 7). First-principle calculation of the positron bound states and pair-annihilation rates of atoms and molecules

The authors have theoretically extended the high-precision first-principle calculation methods such as molecular orbital method and quantum Monte Carlo method to multicomponent systems and implemented them, and have realized the precise calculations of positron affinity and pair-annihilation rate in positron-bound atoms and molecules. Furthermore, by considering the effects of molecular vibrations, the authors obtained good agreement with the latest vibrational Feschbach resonance experiments. As a result of the systematic analysis of positron-bound molecules such as alkali hydride molecules and nitrile compounds, it was found that the positron orbit expanded larger than the electron orbit spatially, and that there was a good correlation between the positron affinity and the permanent dipole moment - dipole polarizability of the parent molecule. (A.O.)