 Bloch wave functions describe the electronic states in a periodic crystal lattice.Bloch functions can be represented as a Fourier series

where Rn denotes an atomic site in a periodic crystal lattice, k is the wave vector of the Bloch wave, r is the electron position, "m" is the band index, and the sum is over all "N" atomic sites.The Bloch wave is an exact eigensolution for the wave function of an electron in a periodic crystal potential corresponding to an energy "E"m (k), and is spread over the entire crystal volume.