Interplay of exciton transfer and relaxation

We have contrasted several methods which can be obtained from the Tokuyama- Mori approach only by serious approximations treating exciton transfer as w ell as relaxation in the simplest model, namely symmetric molecular dimer. We have solved dynamical equations of motion for the density matrix rho of the exciton interacting with a bath. The bath has been simulated by phonons in an infinite linear chain. An exciton-phonon interaction has been taken as the local, linear and weak one. The exciton transfer runs in microscopic "SLE like" models without (mSLE) and with (mSLEr) relaxation slower and, o n the other hand, in the Redfield (RE) model with the secular approximation quicker than in the Tokuyama-Mori (TM) model. Relaxation between extended states + and - is for models mSLEr and RE quicker than in the TM model.