Polaronic

Polarons of Molecular Crystal Model by Nonlocal Dynamical Coherent Potential Method... 

This is the operator (or matrix) equation for the coherent potential v(z). The formal expression for v(z) can be easily written. The exciton polaron is... 

Let us first consider a case of the polaron spectrum when condition (20) is fulfilled so that the nondiagonal matrix elements of the operator F can be neglected, we denote as Vinei the coherent potential in which only the inelastic scatterings are accounted. It is easy show by explicit calculations that... 

The energy spectrum of the exciton polaron as a function of k is obtained by the solution of an equation... 

Polarons of Molecular Crystal Model 451 for complex z with a nonvanishing imaginary part Eq.(25) is written as... 

Such renormalization can be obtained in the framework of the small polaron theory [3]. Scoq is the energy gain of exciton localization. Let us note that the condition (20) and, therefore, Eq.(26) is correct for S 5/wo and arbitrary B/ujq for the lowest energy of the exciton polaron. So Eq.(26) can be used to evaluate the energy of a self-trapped exciton when the energy of the vibrational or lattice relaxation is much larger then the exciton bandwidth. 

It is possible to make elastic scattering corrections to the algorithm (24) in the case of an Einstein phonon spectrum and purely local exciton-phonon coupling. If we calculate the energy of the polaron state at the value E ss nuio only the matrix elements 5 " should be considered in Eqs.(16). In this case... 

In Fig. 1 the absorption spectra for a number of values of excitonic bandwidth B are depicted. The phonon energy Uq is chosen as energy unit there. The presented pictures correspond to three cases of relation between values of phonon and excitonic bandwidths - B < ujq, B = u)o, B > ujq- The first picture [B = 0.3) corresponds to the antiadiabatic limit B -C ljq), which can be handled with the small polaron theories [3]. The last picture(B = 10) represents the adiabatic limit (B wo), that fitted for the use of variation approaches [2]. The intermediate cases B=0.8 and B=1 can t be treated with these techniques. The overall behavior of spectra seems to be reasonable and... 

Semiconductivity in oxide glasses involves polarons. An electron in a localized state distorts its surroundings to some extent, and this combination of the electron plus its distortion is called a polaron. As the electron moves, the distortion moves with it through the lattice. In oxide glasses the polarons are very localized, because of substantial electrostatic interactions between the electrons and the lattice. Conduction is assisted by electron-phonon coupling, ie, the lattice vibrations help transfer the charge carriers from one site to another. The polarons are said to "hop" between sites. 

Eig. 2. Lattice distortions associated with the neutral, polaron, and bipolaron states in poly(p-phenylene). 

According to a large number of experimental studies, the most stable phologen-erated species in the lowest excited stales of conjugated chains are electron-hole pairs bound by Coulomb attraction and associated to a local deformation of the backbone, i.e., polaron-excilons [18]. A good insight into the properties of these species can be provided by quantum-chemical calculations our recent theoretical... 

The decay of photogenerated chaiged excitations such as polarons and bipolar-ons should be bimolecular. In this case, the rate equation is written ... 

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