Solution (source code)

= Solution

The first term is radial kinetic energy from the Laplacian, the second is the attractive <Coulomb's law>[Coulomb potential], and the third is the centrifugal energy from the angular-momentum eigenvalue $L^2=l(l+1)\hbar^2$. Single-valued spherical harmonics require
$$
\boxed{l=0,1,2,\ldots}.
$$