Modelling organic molecular crystals by hybrid quantum mechanical/molecular mechanical embedding

We present a hybrid quantum mechanical/molecular mechanical (QM/MM) embedding scheme to model organic molecular materials. The method employs specialist QM and MM codes as modules in an integrated way that enables the dynamic simulation of large numbers of molecules at a MM level with a smaller fraction treated at a higher QM level of theory. In this preliminary study our QM/MM methodology is applied to the high performance organic (opto)electronic material dithiophene–tetrathiafulvalene (DT–TTF). The QM/MM methodology is tested and confirmed with respect to experiment and previous cluster calculations. The effects of the more realistic treatment of the molecular environment are highlighted.