S. . Purwaningsih, “Ground State Energy of the Helium Using Variational Methods on Trial Wave Functions”, IJSBAR, vol. 54, no. 4, pp. 233–241, Nov. 2020, Accessed: Dec. 16, 2025. [Online]. Available: https://www.gssrr.org/JournalOfBasicAndApplied/article/view/11800