PURWANINGSIH, Sri. Ground State Energy of the Helium Using Variational Methods on Trial Wave Functions. International Journal of Sciences: Basic and Applied Research (IJSBAR), Jordan, v. 54, n. 4, p. 233–241, 2020. Disponível em: https://gssrr.org/JournalOfBasicAndApplied/article/view/11800. Acesso em: 12 oct. 2025.