\begin{equation} \left[ - \frac{\hbar^2}{2 \mu r^2} \frac{d}{dr} \left( r^2 \frac{d}{dr} \right) + V(r) + l(l+1) \frac{\hbar^2}{2 \mu r^2} \right] R(r) = E \, R(r) \qquad (\textnormal{Energy eigenvalue equation}) \tag{1.1} \end{equation}