MEI, Wai-Ning. Systematic Convergence in Applying Variational Method to Double-Well Potential. European Journal of Physics Education, [S.l.], v. 7, n. 2, p. 28-44, feb. 2017. ISSN 1309-7202. Available at: <http://eu-journal.org/index.php/EJPE/article/view/44>. Date accessed: 25 sep. 2020.