Å) for stacks comprising P3HT chains that are 30-mer long (orange circles) versus 6-mer long (blue triangles). The lines are guide to the eyes. In the 30-mer case, increases steadily over three orders of magnitude when an increasing number of neighbors are included in the simulations, reaching a plateau only after sixteen neighbors ( nm). A completely different behavior is predicted for the short (6-mer long) chains where the calculated diffusion coefficient is reduced by a factor when going from nearest-neighbor to full-range interactions.