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2.3 p3ht crystalline bulk phases 23Figure 2.8.: Assembling of P3HT foils. In the h-mechanism (top), twoh-foils assemble in a zigzag-like final structure. In the s-mechanism (bottom), one s-foil stacks on top of a P3HTsemi bulk in the aligned final structure (figure from [3]).By choice, in the calculation of S(q), we take into account aweight f j proportional to the number of electrons for eachatomic species. S(q) is related to the structure factor of thesystem [87].S(q) ∼ 0 when the distribution of atomic positions isdisordered (as occurs in liquids), conversely, when atomsare periodically distributed with period λ, then S(q) ∼ 1for wavevectors satisfying the Bragg condition (i.e. q =2π(nλ) −1 ).This calculation of S(q) has been performed for the differentatomic models of infinite bulks considered in thiswork. The first case is reported in Figure 2.9 left and consistsin an ideal structure formed by s-foils separated by 4Å (hereafter named ideal s-crystal). In the middle panelof Figure 2.9 it is reported the case of the perfect crystalrelaxed at low temperature. Finally, the same bulk equilibratedat room temperature can be found in the right panelof Figure 2.9.Figure 2.10 shows that the order of the crystalline bulkat low temperature (green) is preserved when heated atroom temperature (blue) and only small differences can beappreciated for the S z curves in the π − π direction. Themost relevant difference can be found when comparing thecrystalline bulks to the ideal s-crystal. The peak at q z =