High-Z benchmarking: Probing the sub-eV frontier and an extensive Li-like uranium atomic dataset

Recent theoretical investigations into the excitation energies of the high-Z lithium isoelectronic sequence (Li-like) ions have revealed significant discrepancies Eur. Phys. J. Plus 137 1253 (2022), with deviations between the methods employed reaching up to ∼ 40 eV for U⁸⁹⁺. In this work, we address this issue through a comprehensive study of Li-like uranium (U⁸⁹⁺), calculating the lowest 35 levels of the 1s²nl (n ≤ 6) configurations. We employ two independent relativistic methods: the multiconfiguration Dirac–Hartree–Fock (MCDHF) method implemented in the GRASP2K code, and the relativistic configuration interaction (RCI) method within the Flexible Atomic Code (FAC). Our calculations resolve the discrepancies, achieving excellent mutual agreement and reducing deviations from experimental benchmarks to within ∼ 2 eV. Furthermore, we identify the bottlenecks to achieving sub-eV accuracy for each method in the strong-field, high-Z regime. To the best of our knowledge, this is the most extensive dataset for this ion to date, including excitation energies, lifetimes, and radiative properties for allowed (E1) and forbidden (M1, E2, M2) transitions. Estimated uncertainties for most strong allowed and forbidden transitions remain below 1% and 2%, respectively, rendering this dataset valuable for applications in plasma spectroscopy. The dataset that supported the findings of this study is available in Science Data Bank at https://doi.org/10.57760/sciencedb.32492.