Context. Silver is a key tracer of the weak r-process in late-type stars. However, when the assumption of local thermodynamic equilibrium is relaxed, accurate abundance determinations become even more sensitive to complete sets of reliable transition data. Aims. The aim of this work is to provide accurate and extensive results of excitation energies, radiative transitions, and hyperfine data for Ag I. Methods. The multiconfiguration Dirac-Hartree-Fock (MCDHF) and relativistic coupled-cluster (RCC) methods were used in the present work. The quantitative and qualitative evaluation approach was applied to the MCDHF transition rates to estimate uncertainties using the terminology of the National Institute of Science and Technology Atomic Spectroscopic Database (NIST ASD). Results. Excitation energies, transition data, and hyperfine structure constants were calculated for 18 states up to 4d(10)8s. Fifty-seven electric dipole (E1) transition rates and weighted oscillator strengths were computed, and their uncertainties were estimated to belong to the following NIST ASD classes: four in AA , 12 in A+, five in A, 13 in B+, six in B, and four in C+ with AA <= 1%, A+ <= 2%, A <= 3%, B+ <= 7%, B <= 10%, C+ <= 18%. The remaining transitions, mainly weak transitions involving the 4d(9)5s(2) states, were estimated to be in the E class >50%. The computed lifetimes from both the MCDHF and RCC methods are in good mutual agreement and mostly fall within the error bars of available experimental values from laser-induced fluorescence measurements. The 4d(9)5s(2 2)D(5/2) metastable state, important for establishing the ionization balance, decay through an E2 transition to the ground state. The calculated lifetime is 163 ms. The computed hyperfine interaction constants from the MCDHF and RCC methods are in good agreement and compare well with the scattered experimental constants.

The multiconfiguration Dirac-Hartree-Fock (MCDHF) and relativistic configuration interaction (RCI) methods are used to provide excitation energies, radiative transition data, lifetimes, Landeg-factors, hyperfine interaction constants and isotope shift parameters for the 99 lowest levels of configurations 1s (2)2snl (n <= 7) + 1s (2)2p (2) in beryllium. Compared with available experimental excitation energies, the average difference with the standard deviation is 7.08 +/- 1.14 cm(-1) (0.011% +/- 0.003%), which demonstrates the excellent theory-observation agreement. The uncertainties of the transition rates are estimated based on two independent methods. The present MCDHF/RCI oscillator strengths and those obtained from the explicitly correlated Gaussian method all agree within 2%, except for four transitions affected by strong cancellation effects. For lifetimes, hyperfine splittings and isotope shifts, the present MCDHF/RCI results show good agreement with the few available experimental values, supporting the reliability of our predictions for many states lacking experimental measurements. These comprehensive results can be used in line identification and diagnostics of astrophysical plasmas.

Based on the Multi-Configuration Dirac-Hartree-Fock (MCDHF) method, accurate atomic spectra data including the transition rates, line strengths, and oscillator strengths for the inner-shell excitation configuration 2s2p2(4P)3d in N II ion are reported by taking into account the core-core, core-valence and valence correlation effects as well as the Breit interaction. Good accordance can be found in the comparison with other calculations and measurements. Because the highly excited 2s2p2(4P)3d configuration in N II is larger than the N III thresholds 2s22p2Po3/2 and 2Po1/2 , there exists an autoionization phenomenon. Even the autoionization rates of 2s2p2(4P)3d are much larger than its radiative transition rates. This causes that the energy levels of 2s2p2(4P)3d configuration, especial for the triple states 3P, 3D and 3F, become considerably instable. In addition, there are strong energy level mixing among the 2s2p2(4P)3d configuration and the highly excited configurations 2s22pnl (n = 6; l = p, f, h) with same even parity. These enable the energy levels and their transition rates become sensitive to core correlation effect and Breit interaction.

Using the Multiconfiguration Dirac-Hartree-Fock method as implemented in the General Relativistic Atomic Structure Package, the magnetic dipole and electric quadrupole hyperfine structure constants were determined for the ground and first excited levels of 135,137Ba II isotopes, as well as for 137Ba I and 87Sr II, to assess the robustness of the developed model. This study builds upon and extends previous investigations by examining the levels involved in resonance lines, with the aim of resolving persistent discrepancies in the hyperfine structure of 137Ba II and 87Sr II. New code developments such as the use of natural orbitals, as well as the addition of polarization effects and Configuration State Function Generators, as implemented in GRASPG, were tested for these heavy elements. The developed strategy allowed us to achieve encouraging results that satisfactorily agree with experiments for all studied levels but D5/22 in the 137Ba II isotope. This disagreement was also observed in 135Ba II isotope as well as in 87Sr II. With two valence electrons, 137Ba I is definitely more complex, requiring a multireference approach. Even with the latter, the theory-observation disagreement observed for the hyperfine structure of the low-lying levels remains large in comparison with the alkali-like systems. Possible ongoing developments to remediate this issue are discussed in the conclusions.

Accurate and comprehensive atomic data are essential for the modelling of stellar spectra. Uncertainties in the oscillator strengths of specific lines used for abundance analyses directly translate into uncertainties in the derived elemental abundances; incomplete or biased atomic data sets can impart significant errors in non-local thermodynamic equilibrium (non-LTE) modelling. Theoretical calculations of atomic data are therefore crucial to supplement the limited experimental results. In this work, we present extensive atomic data, including oscillator strengths, transition rates, and lifetimes for 1730 electric-dipole (E1) transitions among 107 levels in neutral sulphur (S I) using the multi-configuration Dirac-Hartree-Fock (MCDHF) and relativistic-configuration-interaction (RCI) methods. These levels belong to the configurations 3p3np (n = 3 - 7), 3p3nf (n = 4, 5), 3s3p5, 3p3ns (n = 4 - 7), and 3p3nd (n = 3 - 6). The accuracy of the computed transition rates is assessed by combining the comparison of the differences in transition rates between the Babushkin and Coulomb gauges with a cancellation-factor (CF) analysis. Approximately 16% of the ab initio results achieved an accuracy classification of A-B, corresponding to uncertainties within 10%, as defined by the Atomic Spectra Database of the National Institute of Standards and Technology (NIST ASD). Applying a fine-tuning technique was found to significantly improve the accuracy of the results in the Coulomb gauge, thereby improving the consistency between the Babushkin and Coulomb gauges; about 24% of the fine-tuned transition data are assigned to the accuracy classes A-B.

Large-scale multiconfigurational calculations are conducted on experimentally significant transitions in Lr I and its lanthanide homologue Lu I, exhibiting good agreement with recent theoretical and experimental results. A single reference calculation is performed, allowing for substitutions from the core within a sufficiently large active set to effectively capture the influence of the core on the valence shells, improving upon previous multiconfigurational calculations. An additional calculation utilizing a multireference set is performed to account for static correlation effects which contribute to the wave function. Reported energies for the two selected transitions are 20 716±550c⁢m−1and 28587±650c⁢m−1for 7⁢𝑠2⁢8⁢𝑠⁢2⁢𝑆1/2→7⁢𝑠2⁢7⁢𝑝⁢2⁢𝑃𝑜1/2and 7⁢𝑠2⁢7⁢𝑑⁢2⁢𝐷3/2→7⁢𝑠2⁢7⁢𝑝⁢2⁢𝑃𝑜1/2, respectively.

The multi-configuration Dirac–Hartree–Fock method implemented in the Grasp2018 package was employed to calculate the magnetic dipole hyperfine interaction constants and electric field gradients of levels in the ground configuration of the neutral bismuth atom. Combining the calculated electric field gradient of the ground state with the measured electric quadrupole hyperfine interaction constant, we extracted the nuclear quadrupole moment for the 209Bi isotope, Q(209Bi)= -422(22) mb. A “world average” value of the nuclear quadrupole moment of this isotope, Q(209Bi)= -422(17) mb, was deduced from the present result combined with a large sample of other theoretical values obtained with elaborate atomic- and molecular-structure calculations.

A methodology based on configuration-state-function generators (CSFGs) has recently been implemented in the General-Purpose Relativistic Atomic Structure Package (grasp) to reduce the computational load of configuration-interaction (CI) calculations Y. T. Li et al., Comput. Phys. Commun. 283, 108562 (2023)10.1016/j.cpc.2022.108562. Large CI calculations can be performed if part of the interaction is treated perturbatively. Here, we present enhancements to the perturbative estimates by implementing blockwise methods, where the blocks are given by configuration-state-functions spanned by CSFGs. We compute excitation energies for 4s24p64d, 4s24p64f, and 4s24p54d2 states in Rb-like W37+ and corresponding transition wavelengths and rates to evaluate the methods. The final relative difference between calculated and experimental wavelengths is 0.01%. Thus, the calculations provide highly accurate values for W37+ properties useful for a variety of applications, including fusion applications.

High-resolution collinear laser spectroscopy of neutron-rich actinium has been performed at TRIUMF's isotope separator and accelerator facility ISAC. By probing the 7s2S01→6d7pP11 ionic transition, the hyperfine structures and optical isotope shifts in Ac+225,226,228,229 have been measured. This allows precise determinations of the changes in mean-square charge radii, magnetic dipole moments, and electric quadrupole moments of these actinium isotopes. The improved precision of charge radii and magnetic moments clears the ambiguity in the odd-even staggering from previous studies. The electric quadrupole moments of Ac225,226,228,229 are determined for the first time.

We demonstrate behaviors of correlation effects in the calculations of atomic properties through two commonly employed many-body methods, namely the multiconfiguration Dirac-Hartree-Fock (MCDHF) and the relativistic coupled-cluster (RCC) methods. Particularly, we have benchmarked excitation energies, electric dipole (E1) matrix elements, magnetic dipole hyperfine structure constants (Ahf), and isotope shift (IS) constants in the singly ionized magnesium (Mg+) systematically at different levels of approximation of both methods. We have also estimated the E1 polarizability of the ground state and lifetimes of the excited states using the E1 matrix elements from both methods. All these results are compared with the experimental values wherever available. We find that the computed results agree well with each other with a few exceptions; in particular, the Ahf and IS constants from the RCC method are found to agree with the measurements better. This comparison analysis would be useful in evaluating the above-discussed properties in other atomic systems using the MCDHF and RCC methods more reliably.