  The orientational dependence of charge carrier mobilities in organic
semiconductor crystals and the correlation with the crystal structure are
investigated by means of quantum chemical first principles calculations
combined with a model using hopping rates from Marcus theory. A master equation
approach is presented which is numerically more efficient than the Monte Carlo
method frequently applied in this context. Furthermore, it is shown that the
widely used approach to calculate the mobility via the diffusion constant along
with rate equations is not appropriate in many important cases. The
calculations are compared with experimental data, showing good qualitative
agreement for pentacene and rubrene. In addition, charge transport properties
of core-fluorinated perylene bisimides are investigated.
