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Pentacene derivative 6,13-dichloropentacene(DCP)is one of the latest additions to the family of organic semiconductors with a great potential for use in transistors.We carry out a theoretical comparative calculation for pentacene,pentathienoacene(PTA,the thiophene equivalent of pentacene)and DCP to gain insights in the theoretical design of organic transport materials.The charge transport parameters and carrier mobilities are investigated from the first-principles calculations and the Marcus electron transfer theory coupled with random walk simulation.Molecular structure and the crystal packing type are essential to understand the differences in transport behaviors.With the effect of molecule modification,significant one-dimensional π-stacks are found within the molecular layer in PTA and DCP crystals.The charge transport along the a axis plays a dominant role for the carrier moblilites in the DCP crystal due to the strong transfer integrals within the a axis.Pentacene shows a large 3D mobility.This is attributed to the relatively uniform electronic couplings,which thus provides more transport pathways.PTA has a much smaller 3D mobility than pentacene and DCP for the obvious increase of the reorganization energy with the introduction of thiophene.It is found that PTA and DCP exhibit lower HOMO levels and better environmental stability,indicating the potential applications in organic electronics.