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3.3 adhesion of a single p3ht molecule on the zinc oxide surface 33Figure 3.2.: Trench grooves (T.G.) and row of dimers (R.D.) in a portionof ZnO.scale model after atomic relaxation based on MPMD is reportedin Figure 3.2 The atomic scale structure of the (10¯10)surface exhibit trench grooves alternated with rows of ZnOdimers (channels), both oriented along the [010] crystallographicdirection. Hereafter in this chapter, the x axis isalways chosen parallel to this [010] crystallographic directionFigure 3.2. As already discussed in chapter 1, in orderto describe the ZnO crystalline surface, we adopt theBuckingham-type potential. This potential describes properlyseveral properties of bulk and nanocrystals such aselastic constants, equilibrium lattice energy, cell parameters,elastic and dielectric constants [72].3.3 adhesion of a single p3ht molecule on thezinc oxide surfaceThe first step in the analysis of the ZnO/P3HT interfaceis the study of the adhesion of a single polymer moleculeon the surface. For this purpose a P3HT molecule composedby 16 monomers is put at different distances fromthe surface with the thiophene rings parallel to it (face-onalignment) and the backbone parallel to the ZnO dimers.The basin of interaction between the ZnO and the P3HTis reported in Figure 3.3, where the unrelaxed energy (calculatedwithout allowing atomic relaxation of the polymerdue to the surface) is reported as a function of the relativedistance between molecule and surface. The minimumof the interaction is found at 3.7 Å and corresponds to