I am reading the fine structure article from Wikipedia at http://en.wikipedia.org/wiki/Fine_structure. Under the heading 'Kinetic energy relativistic correction', we have the following: For the hydrogen atom, V = e2/r. This implies that the expectation of V = -e2/a0n2. Now, I know that you use the unperturbed wavefunction ψ0 to find the expectation of V, but I am not sure of the exact form of ψ0. Any help on this will be greatly appreciated.