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26 p3ht - poly(3-hexylthiophene)Figure 2.11.: Configuration of a P3HT 010 (top) and 100 (bottom)surfaces after a low temperature relaxation (left) and aroom temperature annealing (right).dicates the number of h-foils (growing in the y direction)(see Figure 2.13). For each nanocrystal we perform a relaxationby annealing the system at low temperature. Thedistances between the h-foils (i.e. interdigitation) are reportedin column 3 of Table 2.1. In some cases we studythe nanocrystals resulting by applying the periodic boundaryconditions (pbc) in one or two directions, by allowingrelaxations in the corresponding cell dimensions.First of all we note that there exists a non-monotonic dependenceof the lattice parameter on the size of the nanocrystals.Table 2.1 shows that for pbc along h and s (an infiniteslab of width 16T), the distance between h-foils is the maximum,reaching one of the distances previously identifiedfor the intedigitation of two infinite polymer chains (16 Å).If pbc are applied only along one direction, the interdigitationdistance is smaller (from 13 to 14.6 Å with anexception at 18 Å). Furthermore, whenever the pbc arepresent, the zigzag-like conformation is observed in the relaxednanocrystals similarly to the case of the infinite bulk.As for the finite systems with no pbc, they always giverise to a reduction of the interdigitation distance with respectto the slab, but there is a non-monotonic dependenceon the size. Lower values are found for the nanocrystalscomposed by eight or sixteen s-foils (12.57 Å), while thosecomposed by four s-foils give higher interdigitation distances(up to 16.11 Å). Furthermore, these latter turn outto be the more ordered (see Figure 2.13 compared with Figure2.15). The increase of the size in the z direction (s) is