The motion of electrons in a crystalline solid can in principle be found from the solution of Schrödinger’s equation in quantum mechanics. This results in the electron energy band structure, which describes the relationship between the electron energy E and momentum p in the crystal. The motion of the electron is described by this energy–momentum (E–p) relation, which is known as momentum space.

From de Broglie’s relationship, the momentum p and wavelength λ of the electron are related:

where k is the wavevector; k and p are in direct proportion, related by the rationalized Planck constant. An alternative way of expressing the energy–momentum relation is thus as an energy–wavevector (E–k) relation; this is known as k-space.