When calculating the orbital energy of an electron in a hydrogen-like atom, the orbital velocity is required. However, to derive this value, the equation given is:
\begin{equation*} ZK_{e} e^{2}/r^{2} \end{equation*}
And \begin{equation*}K_{e}\end{equation*}is the atomic number. However, there are plenty of systems that behave with an electron orbital which are non-atomic, like those have an quantum potential well. In these cases, there is no single defined atomic orbitalnumber, so how would one go off calculating this?