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5.2 solvent thf interaction with zno 635.2 solvent thf interaction with zno5.2.1 Interaction between the THF molecule and the ZnO surfaceIn order to investigate the THF-ZnO interaction, a singleTHF molecule on a ZnO surface is studied by a combinationof MPMD and DFT. In particular, MPMD is used tocarefully explore the space of configurations and to findthe stable molecule geometry on the surface. DFT is usedin order to validate and refine the MPMD result.Figure 5.3.: Left: Final configuration of a single THF molecule on aZnO (10¯10) surface, obtained by using DFT techniquesand MPMD (inset). Right: Another perspective of the finalconfiguration of the system, obtained by DFT calculations.Charge density isosurfaces on the (100) plane havebeen superimposed to the atomic configuration.Starting from the THF molecule in different initial positionsand orientations over the surface (with the carbonoxygenring parallel and perpendicular to it) the atomicpositions are relaxed by performing MPMD simulationsat low temperature followed by atomic relaxations basedon the conjugate gradient method. In all cases the oxygenatom of THF binds to a zinc atom on the surface. In the lowestenergy configuration, the molecule turns out to be quasivertical with respect to the surface (see Figure 5.3, inset leftpanel), its plane being perpendicular to the [100] crystallographicdirection. The Zn-O distance is 1.88 Å and thecalculated adhesion energy is found to be as large as 1.12eV. The interaction between the THF molecule and the ZnOas a funcion of the distance is represented in Figure 5.4.This molecule-surface binding is very strong as provedby 10 ns-long room temperature MPMD simulations: althoughseveral different quasi-isoenergetic configurations
64 interaction between tetrahydrofuran solvent and zinc oxideFigure 5.4.: Interaction between a THF molecule and the ZnO surface.are indeed explored (with the molecule quasi vertical asshown in Figure 5.5 left and center or, parallel to the surfaceas shown in Figure 5.5 right), desorption is never observed.Figure 5.5.: Some stable configurations of a THF molecule on the ZnOsurface.In order to validate the MPMD result, the minimum energymolecule-surface configuration (inset Figure 5.3 left)is further relaxed at DFT level (Figure 5.3 left) by usingthe Quantum-ESPRESSO [107] code. The method used isdescribed in section A.3.A Zn-O bond of length 2.1 Å due to the electrostaticinteraction between the positively charged Zn and the negativeoxygen of THF and a partial electronic density overlap,can be observed after the relaxation ( Figure 5.3 rightpanel). Both MPMD and DFT calculation show that themolecule prefers the twist geometry with its plane slightlytilted with respect to the vertical (see Figure 5.3 left andinset). The adhesion energy, calculated by including the
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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
Page 31 and 32: 12 introductionA cheap and environm
Page 33 and 34: 14 introductiondensed phases [63, 7
Page 36 and 37: P 3 H T - P O LY ( 3 - H E X Y LT H
Page 38 and 39: 2.1 mechanism of assembling and mor
Page 40 and 41: 2.2 p3ht assembling and intermolecu
Page 42 and 43: 2.3 p3ht crystalline bulk phases 23
Page 44 and 45: 2.5 nanocrystalline p3ht 25Figure 2
Page 46 and 47: 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 84 and 85: 5.2 solvent thf interaction with zn
Page 86 and 87: 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 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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