E-k diagram of hydrogen atom

The energy of a free (nearly free) electron in a solid (say, metals) is given by $E=h^2k^2/2m$ where k is the momentum vector, h is Planck’s constant and m is the mass of the electron. This expression denotes a parabola. So the E-k diagram of a such an electron is given by,

How will the E-k diagram of a hydrogen atom look like?
In a hydrogen atom, there is one electron. This electron is in under the strong potential of the nucleus. So the energy states are discrete. Probably the above relation does not even hold for this system. So, in such a case, what will be the shape of the E-k curve?