be obtained by assuming the empty lattice approximation, which forms the basis of the band structure model known as the nearly free electron model. Adding repulsive interactions between electrons does not change very much the picture presented here. Lev Landau showed that a Fermi gas under repulsive interactions, can be seen as a gas of equivalent quasiparticles that slightly modify the properties of the metal. Landau's model is now known as the Fermi liquid theory. More exotic phenomena like superconductivity, where interactions can be attractive, require a more refined theory. See also Bloch's theorem Electronic entropy Tight binding Two-dimensional electron gas Bose–Einstein statistics Fermi surface White dwarf Jellium References General Quantum models Condensed matter physics Electronic band structures Electron Arnold Sommerfeld