Reexamination of the Jahn-Teller instability in rquote

The benzene cation H6 has a doublet ground state in hexagonal ring geometry. Therefore a Jahn-Teller (JT) distortion will lower the energy. The present theoretical study yields a model H'bcckel-type Hamiltonian that includes an electron-phonon coupling of the electronic ground state with the two vibrational modes: in-plane ring-bending and C-C bond-stretching. We treat also a third C-H bending mode which has less influence. We obtain the electron-phonon couplings from density functional theory which gives a JT energy lowering of 1 in agreement with previous quantum chemistry calculations. We find a nonadiabatic solution for vibrational spectra and predict frequencies shifts of both the benzene cation and anion.