Bloch theorem. A theorem that specifies the form of the wave functions that characterize electron energy levels in a periodic crystal. Electrons that move in a constant potential, that is, a potential independent of the position r, have wave functions that are plane waves, having the form exp(i k · r).he theorem that the lowest state of a quantum-mechanical system without a magnetic field can carry no current. (solid-state physics). The theorem that, in a periodic structure, every electronic wave function can be represented by a Bloch function.