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A.2 the force field 79Waals interaction modelled on the Lennard-Jones potential[121] :U non−bonded = U vdW + U Coul = ∑ 4ɛ ij(σ ijr ij12−σ ijr ij6) + ∑ q iq j4πɛ 0 r ij(A.20)where ɛ is the depth of the potential well, σ is the finitedistance at which the inter-particle potential is zero and r ijis the distance between the particles. The repulsive term describesthe Pauli repulsion at short ranges due to overlappingelectron orbitals, while the attractive long-range termdescribes the attraction at long ranges (dispersion force).Figure A.2.: Example of Lennard-Jones type potential for two atoms.The interaction between the metal oxide are calculatedby using the Buckingam potential [64, 72]:U buck = A exp(− r ijB ) − C r 6 ij(A.21)where A, B and C are parameters fitted in order to reproduceexperimental data.The non-bonded interaction are the more computationallyexpensive, with the time calculation proportional tothe square of the number of atoms, N 2 , than to N as in thecase of the bonded contributions.An efficient method to spare computational time is representedby the Ewald sum [122]. In this method each pointcharge is surrounded by a charge distribution of the same
80 molecular dynamicsmagnitude and opposite sign that spreads out radially fromthe point charge up to a cutoff distance with a Gaussiandistribution. The interaction is separated in two contribution:the short-range, representing the screening interactionbetween neighboring charges, is calculated in the realspace, while the long-range, representing the cancellingcharge distribution of the same sign as the original charge,is calculated in the reciprocal Fourier space where the convergenceis faster [60]. By using the Ewald summation, thecomputational workload scales as N log(N) instead thanas N 2 .a.3 methodsIn this section we describe the specific technicalities usedin the symulations of the present thesis.The MPMD calculation performed in chapter 2, chapter3 and chapter 4 have been performed by using theDL_POLY code [123], while in chapter 5 we used the Lammpscode [124].The protocol for the relaxation of the systems consistsin low temperature annealings (0.1 ns at 1K) followed byatomic forces relaxations based on standard conjugatedgradients algorithm [125]. The calculations at room temperaturehave been performed by using the NVT or theNPT ensemble, in particular the Nosé-Hoover thermostatand barostat [117, 118].Interactions within ZnO have been described as the sumof Coulomb and a Buckingham-type two-body potential[72, 126]. As for P3HT, the THF and the ZnPC we adoptedthe AMBER force field [62], including both bonding andnonbonding contributions. For hybrid interactions, we useda sum of Coulomb and Lennard-Jones contributions [42].The velocity Verlet algorithm [115] with a time step of 1.0 fshas been used to solve the equations of motion. The atomicpartial charges has been calculated according to the standardAM1-BCC method [127]. A mesh Ewald algorithm[122] has been used for the long-range electrostatic forcesand the Van der Waals interactions have been cutoff at 9.5Å.In chapter 3, first-principles calculations for the transportproperties have been performed within Density Func-
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Università degli Studi di Cagliari
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A C K N O W L E D G M E N T SI woul
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example of a novel class of systems
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C O N T E N T S1 introduction 11.1
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L I S T O F F I G U R E SFigure 1.1
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List of FiguresxiiiFigure 2.15 Init
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List of FiguresxvFigure 4.6Figure 4
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Figure 5.7Figure 5.8Figure A.1Figur
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2 introduction1-3 eV) and the trans
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4 introductionorder in such a compl
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6 introductionprocesses that need t
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8 introduction1.2 physical factors
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10 introductionrecovered by the int
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12 introductionA cheap and environm
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14 introductiondensed phases [63, 7
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P 3 H T - P O LY ( 3 - H E X Y LT H
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2.1 mechanism of assembling and mor
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2.2 p3ht assembling and intermolecu
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2.3 p3ht crystalline bulk phases 23
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2.5 nanocrystalline p3ht 25Figure 2
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2.5 nanocrystalline p3ht 27Table 2.
Page 48 and 49: 2.6 conclusions 29Figure 2.13.: Ini
Page 50 and 51: P O LY M E R / S E M I C O N D U C
Page 52 and 53: 3.3 adhesion of a single p3ht molec
Page 54 and 55: 3.4 p3ht/zno interface 35surface (t
Page 56 and 57: 3.5 p3ht/zno interface: low deposit
Page 58 and 59: 3.6 p3ht/zno interface: high deposi
Page 64 and 65: 3.7 effective model for the transpo
Page 66 and 67: 3.8 conclusions 47As for the low te
Page 68 and 69: T E R N A RY Z N O / Z N P C / P 3
Page 70 and 71: 4.1 self assembling of znpcs on zno
Page 72 and 73: 4.2 polymer interaction with znpcs
Page 74 and 75: 4.3 electronic and optical properti
Page 76 and 77: 4.3 electronic and optical properti
Page 78 and 79: 4.4 conclusions 59ties. The absorpt
Page 80 and 81: I N T E R A C T I O N B E T W E E N
Page 82 and 83: 5.2 solvent thf interaction with zn
Page 88 and 89: 5.3 conclusions 69γ L/L ∼ 0.112
Page 90 and 91: C O N C L U S I O N SIn this thesis
Page 92 and 93: M O L E C U L A R D Y N A M I C SAa
Page 94 and 95: A.1 molecular dynamics 75a.1.2The t
Page 96 and 97: A.2 the force field 77Finally, τ t
Page 100 and 101: A.3 methods 81tional Theory (DFT) l
Page 102 and 103: B I B L I O G R A P H Y[1] http://w
Page 104 and 105: ibliography 85[17] J. D. Servaites,
Page 106 and 107: ibliography 87Zakeeruddin, and M. G
Page 108 and 109: ibliography 89Phys. Chem. Chem. Phy
Page 110 and 111: ibliography 91[65] D. J. Binks and
Page 112 and 113: ibliography 93cells,” Energy Envi
Page 114 and 115: ibliography 95[97] C. Ingrosso, A.
Page 116 and 117: ibliography 97298.15 k,” Journal
Page 118 and 119: ibliography 99charges. am1-bcc mode
Page 120: colophonThis document was typeset u
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