Computational atomic physics continues to play a crucial role in both increasing the understanding of fundamental physics (e.g., quantum electrodynamics and correlation) and producing atomic data for interpreting observations from large-scale research facilities ranging from fusion reactors to high-power laser systems, space-based telescopes and isotope separators. A number of different computational methods, each with their own strengths and weaknesses, is available to meet these tasks. Here, we review the relativistic multiconfiguration method as it applies to the General Relativistic Atomic Structure Package [grasp2018, C. Froese Fischer, G. Gaigalas, P. Jönsson, J. Bieroń, Comput. Phys. Commun. (2018). DOI: 10.1016/j.cpc.2018.10.032]. To illustrate the capacity of the package, examples of calculations of relevance for nuclear physics and astrophysics are presented.

Grasp is a software package in Fortran 95, adapted to run in parallel under MPI, for research in atomic physics. The basic premise is that, given a wave function, any observed atomic property can be computed. Thus, the first step is always to determine a wave function. Different properties challenge the accuracy of the wave function in different ways. This software is distributed under the MIT Licence.

It was recently shown that dielectronic recombination measurements can be used for accurately inferring changes in the nuclear mean-square charge radii of highly charged lithiumlike neodymium [Brandau et al., Phys. Rev. Lett. 100, 073201 (2008)]. To make use of this method to derive information about the nuclear charge distribution for other elements and isotopes, accurate electronic isotope shift parameters are required. In this work, we calculate and discuss the relativistic mass- and field-shift factors for the two 2s2S1/2-2p2P1/2,3/2o transitions along the lithium isoelectronic sequence. Based on the multiconfiguration Dirac-Hartree-Fock method, the electron correlation and the Breit interaction are taken into account systematically. The analysis of the isotope shifts for these two transitions along the isoelectronic sequence demonstrates the importance and competition between the mass shifts and the field shifts.

In the framework of the multiconfiguration Dirac-Hartree-Fock method, we investigate the transition properties of four excited states in the $2p^{5}3s$ configuration of neutral neon. The electron correlation effects are taken into account systematically by using the active space approach. The effect of higher-order correlation on fine structures is shown. We also study the influence of the Breit interaction and find that it reduces the oscillator strength of the ${}^3{P}_1^o{\text{−}}^1{S}_0$ transition by 17$\%$. It turns out that the inclusion of the Breit interaction is essential even for such a light atomic system. Our ab initio calculated line strengths, oscillator strengths, and transition rates are compared with other theoretical values and experimental measurements. Good agreement is found except for the ${}^3{P}_2^o{\text{−}}^1{S}_0$ $M2$ transition for which discrepancies of around 15$\%$ between theories and experiments remain. In addition, the impact of hyperfine interactions on the lifetimes of the ${}^3{P}_0^o$ and ${}^3{P}_2^o$ metastable states is investigated for the ${}^{21}$Ne isotope ($I=3/2$). We find that hyperfine interactions reduce the lifetimes drastically. For the ${}^3{P}_0^o$ state the lifetime is decreased by a factor of 630.

Highly charged ions (HCIs) are promising candidates for the next generation of atomic clocks, owing to their tightly bound electron cloud, which significantly suppresses the common environmental disturbances to the quantum oscillator. Here we propose and pursue an experimental strategy that, while focusing on various HCIs of a single atomic element, keeps the number of candidate clock transitions as large as possible. Following this strategy, we identify four adjacent charge states of nickel HCIs that offer as many as six optical transitions. Experimentally, we demonstrated the essential capability of producing these ions in the low-energy compact Shanghai-Wuhan Electron Beam Ion Trap. We measured the wavelengths of four magnetic-dipole ($M1$) and one electric-quadrupole ($E2$) clock transitions with an accuracy of several ppm with an innovative calibration method. Compared to earlier determinations, our measurements improved wavelength accuracy by an order of magnitude. Such measurements are crucial for constraining the range of laser wavelengths for finding the “needle in a haystack” narrow lines. In addition, we calculated frequencies and quality factors, and evaluated sensitivity of these six transitions to the hypothetical variation of the electromagnetic fine structure constant $\alpha$ needed for fundamental physics applications. We argue that all the six transitions in nickel HCIs offer intrinsic immunity to all common perturbations of quantum oscillators, and one of them has the projected fractional frequency uncertainty down to the remarkable level of ${10}^{-19}$.

We study the prospects of using the electric quadrupole transitions from the ground states of Cu, Ag, and Au to the metastable states ${}^{2}D_{5/2}$ as clock transitions in optical lattice clocks. We calculate lifetimes, transition rates, and systematic shifts and find that they are very suitable for this purpose. In particular, the elements are found to have a blackbody radiation shift that is one to two orders smaller than that of Sr. The Au clock is found to have strong sensitivities to a variation of the fine-structure constant, to effects of scalar dark matter, and to a violation of local Lorentz invariance (LLI). Cu and Ag are also suitable for tests of LLI. We identify two more metastable states (${}^{4}F_{9/2}^o$), one in Cu and another in Au, which can serve as additional clock transitions. The $\alpha$-sensitivity coefficients of the two Au clock transitions are large and have opposite sign. This doubles the overall sensitivity to variation of $\alpha$ and opens the possibility of a $\alpha$-variation test with a single neutral atomic species. We also present more accurate or additional values of the sensitivity to local position invariance violation for several established or proposed clock transitions. These values are important for properly evaluating the effectiveness of clock-clock comparisons.