Effect of Structural Dynamically Induced Disorder on Charge in Molecular Materials

Describing charge carrier anisotropy in small molecule crystalline semiconductors with ab initio methods is challenging because of the weak intermolecular interactions which lead to both localized and delocalized charge interactions. Hopping models (localized) are generally used to describe materials with small charge carrier mobilities, while periodic band models (delocalized) are used to describe materials with high carrier mobilities. Noncovalent interactions between the molecular components mean that dynamic disorder in these materials can have a large impact on the electronic properties of these materials at room temperature. In particular, dynamically induced structural disorder can lead to non-linear changes of the electronic response. Here we build new real temperature computational methodologies based on either Marcus Theory (hopping) or the Boltzmann Transport Equation (band transport) that allow for direct prediction of electronic response of single crystal organics while capturing the weak electrostatic interactions between π-interacting organic molecules, the surrounding crystal environment through periodic symmetry, delocalization of charge in a single calculation, and zero-point energy corrections. In particular, very small atomic displacements can sometimes have a large effect on the localization of electronic density and thus charge transport.