Quantum transport in molecular rings and chains

We study charge transport driven by deformations in molecular rings and cha ins. Level crossings and the associated Longuet-Higgins phase play a centra l role in this theory. In molecular rings, a vanishing cycle of shears pinc hing a gap closure leads, generically to diverging charge transport around the ring, We call such behaviour homeopathic. In an infinite chain, such a cycle leads to integral charge transport, which is independent of the stren gth of deformation. In the Jahn-Teller model of a planar molecular ring, X- p, there is a distinguished cycle in the space of uniform shears? which kee ps the molecule in its manifold of ground states and pinches level crossing . The charge transport in this cycle gives information on the derivative of the hopping amplitudes.