Charge transport polaron models

The formation and transport properties of a large polaron in DNA are discussed in detail by Conwell in a separate chapter of this volume. Further information about the competition of quantum charge delocalization and their localization due to solvation forces can be found in Sect. 10.1. In Sect. 10.1 we also compare a theoretical description of localization/delocalization processes with an approach used to study large polaron formation. Here we focus on the theoretical framework appropriate for analysis of the influence of solvent polarization on charge transport. A convenient method to treat this effect is based on the combination of a tight-binding model for electronic motion and linear response theory for polarization of the water surroundings. To be more specific, let us consider a sequence... 

Gill (1972) was the first to suggest that charge transport in polymers occurred by polaron hopping. The application of polaron theory to transport in polymers was first described by Sahvun (1984). Schein et al. (1990), and Schein (1992). The models described by Sahvun and Schein and coworkers lead to a mobility that is a product of a Boltzmann probability of energy coincidence and the probability a carrier will hop to an adjacent site by thermal activation once... 

We note that the reorganization energy is directly related to such quantities as the polaron binding energy = Xj2) and the dimensionless electron-phonon parameter (K-ph = N(Ep), where N(Ep) is the density of states at the Fermi level [15,23-25,43], The electron-phonon parameter is a key value in the conventional theory of superconductivity. Therefore, the results discussed before are especially relevant in the development of adequate polaron models to understand superconductivity and charge transport in organic molecular systems. 

The relevance of the studies discussed to electrochemical charge transport is that similar models can also be applied to the electrochemical situations. Our concern in the electrochemical context is the moderately doped state, in which our applications are envisaged. For the moderately doped state at room temperature, bipolaron or polaron bands are theoretically not expected to form. Hence the conduction is expected to be activated. 

In the case of weakly FeCla doped PPPs, the dc conductivity (Cdc) was proportional to T n 10). This result, which is very different from Mott s relationship, was interpreted as being due to hopping and fitted a relationship involving a slightly modified Kivelson model [228] between polarons and bipolar-ons. With more heavily doped PPPs, the charge transport mechanism changed dramatically, and Cdc was then given by Mott s relationship corre-... 

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