Non-Relativistic QED (NRQED) Calculations of Atomic Ionization Potentials and the Future of the NRQED Method in Small Molecule Astrochemistry

The canonical computational approach of quantum electrodynamics (QED) is not practical for bound states involving multiple correlating electrons. As a result, newer forms^1-3 of QED have been developed to tackle few-body atomic problems and are now being applied to the molecular domain. I will discuss a low-energy reconfiguration of QED especially suitable for molecules, namely non-relativistic QED (NRQED)³, applicable to few-electron, low-Z states. In particular, I will focus on work I am doing to establish the utility of this method for increasingly relativistic bound states, by examining the convergence of computed isoelectronic ionization sequences to experiment. This includes calculation of leading-order relativistic and radiative corrections, as well as consideration of computational subtleties including the Bethe logarithm, finite nuclear mass/size effects, singular expectation values, and α⁶ order corrections.⁴ In doing so, future applications of NRQED to small molecule astrochemistry are suggested, focusing on transitions which may be calculated with accuracies comparable to spectroscopic uncertainties.


1. Shabaev, Phys. Rep., 356, 119
2. Lindgren, Can. J. Phys., 83, 183
3. Caswell, Phys. Lett. B, 167, 437
4. Patkos, Phys. Rev. A, 100, 042510