Exciton polarons in molecular aggregates: a dynamical coherent potential approximation approach

A dynamical coherent potential approximation (DCPA) is formulated within the Hartree approximation for an exciton interacting with phonons. Two-exciton polaron spectra can be calculated by the present method. For the one-exciton interacting with Einstein phonons by a linear short-range coupling, it is shown that the present formulation is equivalent to the well-known single-site approximation DCPA. For a nonlocal exciton–phonon coupling, the result is compared with a variational band theory and they show good agreement.