The Jahn - Teller Effect

The Jahn – Teller effect is a set of effects associated with the interaction of the orbital states of electrons and distortions of the crystal lattice field. It was named after G. Jan and E. Teller , who formulated in 1937 a theorem according to which any nonlinear configuration of atoms containing degenerate states of electrons is unstable with respect to deformations that reduce its symmetry . The degeneracy of electronic states can be due to the presence of high symmetry in the molecule or crystal lattice, and the distortion of its field can be associated with vibrational motions of atomic nuclei or distortions of the lattice itself. The interaction of electronic states with distortions leads to the removal of degeneracy and a decrease in symmetry.

Distinguish between the static and dynamic effects of Jan - Teller. The first is said if the interaction between electrons and vibrations of nuclei leads to the formation of local deformations and a change in the symmetry of the crystal, and the second - if so-called vibronic states are formed (specific coupled vibrations of nuclei and electrons).