Optic polaron, description

The absorption spectrum of the cationic dimer, as computed at the AMl/FCI level (with up to 26 molecular orbitals in the active space) and INDO/SDCI (with all possible single excitations within the TT-manifold and double excitations over 22 ir-orbitals), is shown in comparison to that of the one-chain polaron in Figure 1.14. The optical features discussed below are common to the descriptions provided by the AMl/FCI and INDO/SDCI formalisms. 

To understand the transition to supersonic velocities we also make use of a description of the lattice in terms of both optical and acoustic order parameters. Here, we study a strictly ID model that is a direct map of the fPA structure. However, as far as the properties of the drifting polaron are concerned, the model is more general and quantitatively describes these properties in other polymeric systems, e.g., poly(paraphenylene vinylene) or polythiophene. In the ID model, the displacement of the lattice sites entering Equation 2.14 and Equation 2.16 is described by a single variable u . In the description of the geometry of conjugated polymers, fPA in particular, it is common to study a smoothed atomic displacement order parameter. This optical order parameter is given by... 

In ID the lattice deforms around the electron and loced.ises the electron to form a polaron. The ii portant deformation is acoustic, in udiich the density of the lattice changes optic deformations occur also but are not important in the polaron motion. The mathematical description of the polaron is like that of solitary waves. The Solitary wave Acoustic Polaron (SWAP) has a very large effective mass its kinetic velocity is small. Horeover it cannot move at a velocity greater than S as its kinetic velocity approaches S the acoustic deformation increases and the SNAP mass increases. In addition back scattering is very rare. So the SWAP kinetic and drift velocities are equal. 

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