Particle-hole configuration interaction and many-body perturbation theory: application to Hg+

TL;DR

This paper extends the CI+MBPT method to include electron holes non-perturbatively, enabling accurate treatment of systems with hole configurations, exemplified by Hg+ optical clock transitions, and analyzing their sensitivity to fundamental constant variations.

Contribution

The method is innovatively extended to treat electron holes non-perturbatively, improving accuracy for complex atomic systems like Hg+ and related applications.

Findings

Achieved ~1% accuracy for Hg+ transition energies.

Successfully modeled valence-hole and particle-hole systems.

Reinterpreted laboratory limits on the fine-structure constant's variation.

Abstract

The combination of configuration interaction and many-body perturbation theory methods (CI+MBPT) is extended to non-perturbatively include configurations with electron holes below the designated Fermi level, allowing us to treat systems where holes play an important role. For example, the method can treat valence-hole systems like Ir$^{17+}$, particle-hole excitations in noble gases, and difficult transitions such as the $6s \rightarrow 5d^{-1}6s^2$ optical clock transition in Hg$^+$. We take the latter system as our test case for the method and obtain very good accuracy (~1%) for the low-lying transition energies. The $\alpha$-dependence of these transitions is calculated and used to reinterpret the existing best laboratory limits on the time-dependence of the fine-structure constant.