Electron self-energy corrections using the Welton concept for atomic structure calculations

The high level of accuracy achieved by atomic experiments in recent time has shone a spotlight on the need for a similarly high level of accuracy in atomic structure calculations, and in particular, QED prediction. A method of electron self-energy correction originally derived from the Welton idea by Lowe et al. (2013) (LCG-Welton method) has now been fully incorporated into the popular atomic structural package, GRASP2K, which we have introduced in this paper. A series of benchmark tests and results are presented, which enables the comparison of the implementations of different versions of GRASP2K, and the implementations on different platforms or operating systems. Test results presented in this paper demonstrate that these new implementations maintain the overall consistency and stability of the program across various platforms, while at the same time improve the accuracy of final energies. Our calculations for hydrogenic Ly alpha(1,2) transitions show excellent agreement with experiment, to within less than 0.5 eV. On helium-like systems, our calculations show an improvement from the previous GRASP2K screening method. The new results from electronic self-energy contribution using the LCG-Welton method is more consistent with current standards in the literature, where they now fit within experimental variability of up to 0.1 eV. An option for users to adjust the gauge factor in the electric component of the transition rate has also been added to facilitate further investigation of this particular topic.