INTERPLAY OF EXCITON OR ELECTRON-TRANSFER AND RELAXATION .1. MORI APPROACH

Mori theory together with canonical transformation but with quantities of interest remaining untransformed is applied to the exciton- or ele ctron-phonon system with site-diagonal linear coupling and full excito n or electron density matrix; finite concentrations of the carriers ar e admitted. Partial small polaron transformation is used which allows to investigate relaxation of initially partially relaxed systems witho ut initial-condition terms. The result is applied, in the lowest order in the coupling, to a particle on a symmetric dimer. Coefficients sug gested in a recent generalization of the Haken-Strobl-Reineker model a re identified. The theory surprisingly, is found to be, in the above o rder, insufficient to yield a loss of coherence of carrier propagation with increasing time, though standard Markovian treatment suggests th e opposite. A new type of a so far unnoticed drawback, typical of fini te-order time-convolution theories, which is connected with the infini te memory of the initial lattice relaxation becomes conspicuous.