Testing quantum electrodynamics in the lowest singlet states of beryllium atom

TL;DR

This paper presents high-precision theoretical calculations of beryllium atom energy levels, including QED effects, enabling tests of quantum electrodynamics and determination of nuclear charge radii.

Contribution

It provides the first highly accurate QED-inclusive calculations for beryllium's lowest singlet states, approaching the precision of three-electron atom computations.

Findings

Theoretical ionization potential: 75,192.699(7) cm⁻¹.

Transition energy for 2¹P → 2¹S: 42,565.441(11) cm⁻¹.

Results enable tests of QED and nuclear charge radius determination.

Abstract

High-precision results are reported for the energy levels of $2{^1S}$ and $2{^1P}$ states of the beryllium atom. Calculations are performed using fully correlated Gaussian basis sets and taking into account the relativistic, quantum electrodynamics (QED), and finite nuclear mass effects. Theoretical predictions for the ionization potential of the beryllium ground state $75\,192.699(7) \icm$ and the $2{^1P} \rightarrow 2{^1S}$ transition energy $42\,565.441(11) \icm$ are compared to the known but less accurate experimental values. The accuracy of the four-electron computations approaches that achieved for the three-electron atoms, which enables determination of the nuclear charge radii and precision tests of QED.