"The
Jahn-Teller (J-T) theorem states that in molecules/ ions that have a degenerate
ground-state, the molecule/ion will distort to remove the degeneracy. This is a
fancy way of saying that when orbitals in the same level are occupied by
different numbers of electrons, this will lead to distortion of the molecule.
For us, what is important is that if the two orbitals of the eg
level have different numbers of electrons, this will lead to J-T distortion. Cu(II) with its d9
configuration is degenerate and has J-T distortion."
In Quantum point of view, electrons are dynamically hoping between different orbitals. To form a unequal occupation between two degenerate orbitals, a fluctuation is required. So this is like the van der Waals interaction, is essentially a Casimir effect.
However, to distort the lattice, maybe we need to have ion lattice relaxation time is shorter than the hoping/fluctuation time.
Is this the correct picture?
