A Pedestrian Approach to Atomic Structure, Data and Behavior

The computation of atomic energies, cross sections and other observables covers a wide spectrum of applications, from rapid estimates to large-scale calculations and the modeling of atomic behavior. These computations are useful and indispensable in astrophysics, plasma and radiation physics, spectroscopy and several related fields. Although various atomic codes exist and have been broadly applied, their complexity often limits accessibility for exploratory, pedagogical, or interdisciplinary use. In this survey, we introduce a pedestrian approach to atomic computations, implemented as a simplified interface within Jac, the Jena Atomic Calculator. The interface allows users to specify, execute, and analyze complete atomic computations—including electronic structure, decay rates and other atomic properties—with minimal input and transparent, inspectable output. This interface is built on the relativistic Dirac–Coulomb Hamiltonian, whose bound-state solutions are obtained with the multiconfiguration Dirac–Hartree–Fock (MCDHF) method; the Breit interaction and leading QED corrections are available as perturbative additions. The pedestrian approach is demonstrated through the computation of level energies and photoionization cross sections of argon, for which physically meaningful results are obtained within a few lines of Julia code. Our pedestrian interface lowers the entry barrier for non-specialists and serves as a rapid-prototyping tool for experienced atomic physicists; it is fully consistent with Jac’s modular architecture and enables one to extend the workflow step by step towards the full power of the Jac tools. The approach also supports teaching relativistic atomic theory and enables one to reproduce published results through self-contained, executable Julia code examples.