Free-basis-set method to describe the helium atom confined by a spherical box with finite and infinite potentialsCésar Martínez-Flores, Michael-Adán Martínez-Sánchez, Rubicelia Vargas and Jorge GarzaEur. Phys. J. D, 75 3 (2021) 100DOI: https://doi.org/10.1140/epjd/s10053-021-00110-x