The
Jahn–Teller effect, sometimes also known as
Jahn–Teller distortion, describes the geometrical distortion of
molecules and
ions that is associated with certain electron configurations. This
electronic effect is named after
Hermann Arthur Jahn and
Edward Teller, who proved, using
group theory, that orbital nonlinear spatially degenerate molecules
cannot be stable. The
Jahn–Teller theorem essentially states that any nonlinear molecule with a spatially
degenerate electronic ground state will undergo a geometrical distortion that removes that degeneracy, because the distortion lowers the overall energy of the species. For a description of another type of geometrical distortion that occurs in crystals with substitutional impurities see article
off-center ions.