Electronic conductivity in Molecular Crystals: An Alternative to the Bloch-Function Approach

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Abstract
Bloch functions are not good basis functions for molecular crystals in high electric fields. When the interaction with the electric field is large with respect to next‐neighbor interactions, it is better to use wave‐functions which are localized over molecular sites as basis functions. A treatment of electronic mobility and diffusion in molecular crystals using quantum mechanical transition probabilities between localized energy levels and considering only nearest‐neighbor interactions is developed. The asymmetry of the potential function, caused by the electric field, and the conservation of energy during transport are considered. The mobility is found to be independent of temperature, and the diffusion constant proportional to temperature. The magnitude of the diffusion constant calculated from phonon‐induced transitions is quite reasonable (4.6×10—3). Photon‐induced transitions do not appear to be important.