Evaluation of the External Reorganization Energy of Polyacenes

The external reorganization energy for hole transport in naphthalene, anthracene, tetracene, pentacene, and rubrene is computed using a polarizable force field. The importance of this very small contribution to the Hamiltonian of the Molecular crystal in the context of charge transport modeling is discussed. The effect of the force field parameters and the size of the model system on the computed reorganization energy is analyzed. The results are rationalized with a simple model which clarifies the fundamental differences between the external reorganization energy in the solid and liquid phases.