Beltrán-López, L. G.-T. and V. “The Non-Additive Potential in the He$_3$ System Within the LCAO-MO-SCF Approximation”. Revista Mexicana De Física, vol. 23, no. 3, Jan. 1974, pp. 301-18, https://rmf.smf.mx/ojs/index.php/rmf/article/view/1052.