Polaronic clusters

The geometries used for the soliton and polaron cluster are shown in Figure 9.6. 

Finally, out-of-plane force constants should be discussed briefly. Until now only one recent study > included also the out-of-plane motions of the hydrogen and carbon atoms. In the work of Peluso et these motions were included because they may be useful in the interpretation of additional new bands in the infrared spectrum of doped PA. The scale factor for the out-of-plane C-H bending force constant has been obtained by comparing the MNDO results and experimental frequencies symmetry decoupling of these modes from the in-plane modes makes this procedure possible. Calculations confirmed the conjecture a large lowering of out-of-plane force constants was found for both soliton models and for the charged polaron cluster. 

The interaction between a charged point defect and neighboring magnetic ions in magnetically doped thin films has been described in terms of a defect cluster called a bound magnetic polaron (Fig. 9.5a). The radius of a bound magnetic polaron due to an electron located on the defect, r, is given by... 

This approximation has a philosophical and mathematical resemblance to the linked-cluster expansion that has been applied successfully to the small polaron problem. The linked-cluster expansion is an exponential resummation of... 

Besides the mentioned aperiodicity problem the treatment of correlation in the ground state of a polymer presents the most formidable problem. If one has a polymer with completely filled valence and conduction bands, one can Fourier transform the delocalized Bloch orbitals into localized Wannier functions and use these (instead of the MO-s of the polymer units) for a quantum chemical treatment of the short range correlation in a subunit taking only excitations in the subunit or between the reference unit and a few neighbouring units. With the aid of the Wannier functions then one can perform a Moeller-Plesset perturbation theory (PX), or for instance, a coupled electron pair approximation (CEPA) (1 ), or a coupled cluster expansion (19) calculation. The long range correlation then can be approximated with the help of the already mentioned electronic polaron model (11). 

In summary, over a large range of interchain distances, the most stable species photogenerated in the lowest excited state of clusters formed by identical molecules are excitons mostly with an intrachain character. The calculations also show that polaron-pairs, also referred to as interchain excitons (corresponding to a posi-... 

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