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Charge Transport in DNA - Insights from Simulations
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2.6ChargeTransfer inDNA can be called hops or switches. The key issue to be solvedhere is to calculate the probabilityof suchahop inevery timestepunder thegivencircumstances. The implementation used in this work is based on the SH algorithm by Persico et al. [104]. This algorithmuses the local diabatization of the adiabatic states of the system. The advantage of this is a stable representation of adiabatic states in regionsof avoidedcrossingor conical intersections. In the implementedsetup, theeigenproblemof theexcess charge is solved inevery time step. From this, thewave-function of the excess charge is given as a combi- nationof the adiabatic states. Then thediabatic states are redefined tobe identical with the ones at the beginning of the time step. The TDSE is then solved for this locallydiabaticbasis topropagate thewave-functionof theexcess charge. Thecru- cial step here is the calculation of the probability to hop from the current state to one of the calculated new states from the populations. The transition to another state is thendeterminedbydrawinga randomnumber. This isanalternativetopropagatingthewave-functionwiththemean-fieldmethod. The rest of the simulationprotocol is identicalwith that in themean-fieldmethod. Here again, the propagatedwave-function can be transferred directly to the clas- sicalMDsimulationby themapping to the atomic charges. The advantage of this setup is that there is no over-delocalization issue like in themean-field approach. However, in thismethodtheCGHamiltonianhas tobediagonalized. All represen- tationsof thequantumsystemconsistof individual states. Therefore it isnecessary to choosea representation inadvance. There is no artificial CTwhen the electronic couplings are very lowor even zero. Andfinally, themicroscopicalreversibility is fulfilled,againincontrast tothemean- fieldapproach,. Unfortunately, also the current implementation of the SH method suffers from some issues, which will be outlined shortly. After a surface hop, the velocities of the classicalMMatoms are not rescaled. This possiblymeans that there is no energyconservation. Another issueare the classically forbidden transitions,which are not treated in our setup. The quantum system is supposed to have enough energyat any time for thehop tooccur. 37
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Charge Transport in DNA Insights from Simulations
Titel
Charge Transport in DNA
Untertitel
Insights from Simulations
Autor
Mario Wolter
Verlag
KIT Scientific Publishing
Datum
2013
Sprache
englisch
Lizenz
CC BY-SA 3.0
ISBN
978-3-7315-0082-7
Abmessungen
17.0 x 24.0 cm
Seiten
156
Schlagwörter
Charge Transport, Charge Transfer, DNA, Molecular Dynamics, Quantum Mechanics
Kategorien
Naturwissenschaften Chemie

Inhaltsverzeichnis

  1. Zusammenfassung 1
  2. Summary 3
  3. 1 Introduction 5
  4. 2 TheoreticalBackground 11
    1. 2.1 MolecularMechanics 11
    2. 2.2 MolecularDynamicsSimulation 13
      1. 2.2.1 Solving theEquationsofMotion 14
      2. 2.2.2 ThermodynamicEnsembles 15
    3. 2.3 QuantumChemistry 18
      1. 2.3.1 DensityFunctionalTheory 18
      2. 2.3.2 ApproximativeDFT–Density-FunctionalTight-Binding 21
    4. 2.4 DynamicsofExcessCharge inDNA 24
      1. 2.4.1 TheMulti-ScaleFramework 25
      2. 2.4.2 TheFragmentOrbitalApproach 26
    5. 2.5 ChargeTransport inDNA 29
      1. 2.5.1 Landauer–BüttikerFramework 29
    6. 2.6 ChargeTransfer inDNA 32
      1. 2.6.1 Basics ofChargeTransfer 32
      2. 2.6.2 Non-adiabaticPropagationSchemes 34
  5. 3 SimulationSetup 39
    1. 3.1 TheDNAMolecule 39
      1. 3.1.1 InvestigatedDNASequences 42
    2. 3.2 MDSimulationofDNA 44
    3. 3.3 DNAunderMechanical Stress 45
    4. 3.4 MicrohydratedDNA 46
  6. 4 DNAUnderExperimentalConditions 49
    1. 4.1 FreeMDSimulations 50
    2. 4.2 TheStructuralChangesofDNAuponStretching 51
    3. 4.3 IrreversibilityofDNAStretching inSimulations 56
    4. 4.4 Effects ofLowHydration 58
    5. 4.5 Effects ofDecreased IonContent 62
    6. 4.6 Effect ofWater and Ionson theStretchingProfileofDNA 64
    7. 4.7 Conclusion 67
  7. 5 ChargeTransport inStretchedDNA 69
    1. 5.1 InvestigatedSequences andStructures 69
    2. 5.2 ChargeTransportCalculations 71
    3. 5.3 SequenceDependentChargeTransport 73
    4. 5.4 DetailedStructuralDifferences 74
    5. 5.5 Conclusion 76
  8. 6 ChargeTransport inMicrohydratedDNA 79
    1. 6.1 InvestigatedSequences andStructures 79
    2. 6.2 ChargeTransferParameters 80
    3. 6.3 ChargeTransportCalculations 84
    4. 6.4 DirectDynamicsofChargeTransfer 86
    5. 6.5 Conclusion 87
  9. 7 AParametrizedModel toSimulateCT inDNA 89
    1. 7.1 Creating theElectronicCouplings 90
    2. 7.2 Modeling the IonizationPotentials 93
    3. 7.3 TestingwithChargeTransportCalculations 97
    4. 7.4 ChargeTransferExtensions 98
    5. 7.5 TestingwithChargeTransferMethods 102
    6. 7.6 Conclusion 103
  10. 8 Conclusion 105
  11. Appendix 111
  12. A DNAUnderExperimentalConditions 111
    1. A.1 TheStructuralChangesofDNAuponStretching 111
    2. A.2 Effect ofLowHydrationandDecreased IonContent 112
    3. A.3 StretchingofMicrohydratedDNA 116
  13. B CTinMicrohydratedDNA 117
    1. B.1 HelicalParameters -CompleteOverview 117
    2. B.2 ElectronicCouplings 118
    3. B.3 IonizationPotentials 119
    4. B.4 ESP InducedbyDifferentGroupsofAtoms 122
    5. B.5 DistanceofChargedAtomGroups fromtheHelicalAxis 123
  14. List ofPublications 137
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Charge Transport in DNA