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4.2 polymer interaction with znpcs functionalized zinc oxide 53Figure 4.4.: Building of a layer of ZnPcs on the ZnO surface startingfrom a single relaxed molecule.4.2 polymer interaction with znpcs functionalizedzinc oxideOnce the ZnO surface fully covered by ZnPcs is obtained,the further step is to investigate the interaction with a singlepolymer molecule. We want to study how the ZnPcsaffects the interaction with the substrate. For this purposewe used a oligomer composed by 8 thiophenes (see Figure4.5 left). We investigated the interaction between thepolymer and the ZnO/ZnPcs surface by calculating the attractionbasin reported in Figure 4.5 top right, where theenergy is calculated as a function of the relative distancebetween the polymer and the surface.At each distance from the substrate the energy was minimizedwith respect to different orientations of the molecule.The calculated energy curve exhibits a minimum for polymersubstratedistance of about 3 Å and an interaction rangeof about 1 nm. By fully optimizing the minimum energyconfiguration we obtain the lowest energy structure of the