Weak exciton-phonon coupling coherent excitons

ancj are the creation and annihilation operators, respectively, for phonons in mode q = (q, r), where q denotes the vector of the phonon and r is the branch label. The energy of these phonon modes is given by u q. Furthermore, the single-molecule Hamiltonian as well as the intermolecular transfer interaction are still considered to be operators in phonon space. 

As can be seen from eqn (14.8), the calculation of the tensor reduces to the calculation of two-particle correlation functions. The lack of sufficiently detailed data on the exciton band structure and the exciton-phonon coupling constants considerably complicates the accurate calculation of the two-particle correlation functions and the exciton diffusion coefficients. However, the temperature dependence of this coefficient differs significantly for coherent and incoherent excitons (see below). Therefore, studying the temperature dependence of diffusion has always been an important tool to analyze the character of the energy transfer in molecular crystals. In the remainder of this chapter, we will focus on the main characteristics of the diffusion constant and its temperature dependence 

3 Weak exciton phonon coupling coherent excitons 

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WEAK EXCITON-PHONON COUPLING COHERENT EXCITONS... 

If the exciton-phonon coupling is sufficiently weak, the solution of the equation for the correlation function (B (t)Bm(t)B, (0)Bm (0)) is equivalent to the solution of the Boltzmann equation (11). In this coherent limit, the exciton states of... 

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