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A.3 methods 81tional Theory (DFT) level. The estimate of the electroniccoupling for cofacial dimers has been obtained using theso-called "energy splitting in dimer" method [95]. In thismethod the transfer integral for holes can be computedevaluating the energy difference between the orbitals resultingfrom the overlap of the highest occupied molecularorbitals of the two interacting molecules: J αβ = (ɛ HOMO −ɛ HOMO−1 )/2, where ɛ HOMO and ɛ HOMO−1 are the energiesof the two highest occupied molecular orbitals of the dimer.We used the gradient-corrected PBE density-functional [128]together with a plane-wave basis set and ultrasoft pseudopotentialsas implemented in the CPMD [129] programpackage; to account for dispersion interactions we used theempirical dispersion correction proposed by Grimme [108],that adds a Van der Waals-type term scaling as R −6 into thetotal energy of the system.As for the ab initio methods used in chapter 4, DFT+Ucalculations have been performed by using the Quantum-ESPRESSO package[107]. Total energies have been calculatedby using ultrasoft pseudopotentials[130], by expandingKohn-Sham eigenfunctions on a plane-wave basis set.The cutoff has been set at 35 Ry on the plane waves and at280 Ry on the electronic density. The electronic propertiesof the ZnO/P3HT system, of the ZnO/ZnPc system, and ofthe double-interface ZnO/ZnPc/P3HT system have beeninvestigated by analyzing the electronic eigenvalues calculatedat the Γ point. The exchange-correlation functionalhas been obtained by adding an ab initio non-local vander Waals correlation contribution[131, 132] to the semilocalgradient-corrected PBE functional[128]. An Hubbard Ucorrection [133, 134] has been applied to the Zn 3d and O2p atomic shells, thus allowing for an optimal position ofZnO band edges with respect to the molecule and polymerHOMO-LUMO levels. A P3HT oligomer, formed by fourmonomers has been used to simulate the properties of thepolymer. Finally, optical absorption spectra ranging fromthe near-IR to the near-UV regions have been calculatedby using a recent approach to the solution of the Bethe-Salpeter equation within the framework of time-dependentdensity matrix perturbation theory (TDDFPT) [135, 136].In chapter 5, the interaction between the single THF moleculeand the ZnO surface at DFT level have been perfomed by
82 molecular dynamicsusing the Quantum-ESPRESSO [107] code. We used Vanderbiltultrasoft pseudopotentials with the Perdew-Burke-Ernzerhof (PBE) version of the generalized gradient approximation(GGA) exchange-correlation functional [128] .Kohn-Sham eigenfunctions have been expanded on a planewavebasis set by using cutoffs of 30 Ry on the plane wavesand of 300 Ry on the electronic density. The Grimme [108]correction has been used to include the effects of dispersioninteractions. In addition to the 13 atoms of the THF,the surface cell contained a 3x2 slab formed by 4 atomiclayers of ZnO (48 atoms) and 30 Å of empty space. Theelectronic properties of the system have been investigatedby analyzing the electronic eigenvalues calculated at the Γpoint.
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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.
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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 98 and 99: A.2 the force field 79Waals interac
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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