Dynamical Jahn-Teller instability in metallic fullerides

The ground state of metallic fulleride K$_3$C$_{60}$ is investigated {\it ab initio} with a concomitant self-consistent treatment of the electron correlation and the Jahn-Teller (JT) effect [1]. The potential energy surface has two minima with and without JT distortion. It is found that static JT instability on C$_{60}$ sites is favored when the intrafullerene electron repulsion $U > $ 650 meV. At the same time the amplitude of variations of the band energy as function of the direction of JT distortions are found to be much smaller than the energy gain from dynamical delocalization of JT deformations implying dynamical JT instability on C$_{60}$ sites. The latter develops already at $U = $ 500 meV, while for $U > $ 600 meV the amplitude of JT deformation approches the value for isolated C$_{60}^{3-}$, leading to strong enlargement and complete removal of degeneracy of the LUMO band. \\[4pt] [1] N. Iwahara and L. F. Chibotaru, submitted.