Gning, M. T. “Calculations of Energy Levels of the Singly Excited States (1snl) 1,3Lp for Heliumlike Ions With Z ≤ 12”. European Journal of Applied Physics, vol. 4, no. 6, Nov. 2022, pp. 11-19, doi:10.24018/ejphysics.2022.4.6.219.