Su-Schrieffer-Heeger

So far we have outlined the conceptual framework in which we discuss charge transfer in organic semiconductors. It is based on a molecular picture where the molecular unit is considered central, with interactions between molecular units added afterwards. For amorphous molecular solids and for molecular crystals this approach is undisputed. In the case of semiconducting polymers, a conceptually different view has been proposed that starts from a one-dimensional (ID) semiconductor band picture, and that is generally known as the Su-Schrieffer-Heeger (SSH) model [21-24]. 

In the one-dimensional limit, the coupling to acoustic phonons is at the heart of the Su-Schrieffer-Heeger (SSH) Hamiltonian [21] ... 

The Su Schrieffer Heeger (11) Hamiltonian for one extra electron added to an insulator is... 

Wan et al.236 have used the Su-Schrieffer-Heeger model to calculate a for five different C78 isomers and predict a great variation of optical properties with symmetry and shape. 

One of the interesting predictions of the Su-Schrieffer-Heeger model [158, 159] is that the electronic excitations are closely related to the topological distortions of the conjugated polyene chain. It is predicted that solitons are the elementary excitations both for optical... 

Fig. 2.7. The bond stretching mode of trana-CB.x projected onto the a -axis. 2.8.2 The Su-Schrieffer-Heeger model...

In a TT-electron theory the ion represents the CH group, so there are three ionic degrees of freedom per unit cell. These ionic degrees of freedom may be formally represented as collective, normal modes. Su, Schrieffer, and Heeger, in their treatment of frans-polyacetylene, introduced a simplification to this problem (Su et al. 1970). This simplification was to consider only the normal mode that predominantly couples to the tr-electrons. For polyacetylene this is the carbon bond stretching vibration. Thus, projecting the ionic coordinates onto the chain axis, denoted by the x-axis, we have the Su-Schrieffer-Heeger (SSH) Hamiltonian, defined as,... 

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