Abstract
A general consideration is made of the vibronic coupling in a (h(u)(+))(2) circle times h(g) Jahn-Teller system, that is to say, a system in which two holes of H-u symmetry are coupled to vibrations of h(g) symmetry. We find that the resulting high-spin states may undergo spontaneous distortion into species exhibiting one of the following four possible symmetries: D-5d, D-3d, D-2h or C-2h.
The system may be viewed as a first approximation to a C-60(2+) ion, but our intention here is to make a general consideration of the model without application to any specific molecular system. Coulombic interactions between holes, which must be important in real systems, are therefore ignored throughout. However, they could be included in the model, if required, using the method described in an earlier work [I.D. Hands, J.L. Dunn, W.A. Diery, C.A. Bates, Phys. Rev. B 73 (2006) 115435].
For each of the different symmetry types, projection operators are used to create symmetry-adapted states (SASs) that give a good account of the states of the system over a wide range of coupling strengths. These SASs are used, in turn, to derive energies for the vibronic states. (c) 2007 Elsevier B.V. All rights reserved.