2009全国功能材料量子设计和量子物理研究生培训PPT-1.ppt 41页

'MaterialsModelingandSimulationfromtheatomictothemesoscopicscalesFengLiuDepartmentofMaterialsScienceandEngineeringUniversityofUtah,SaltLakeCity,UT OverviewofComputationalMaterialsScienceFirst-principles(abinitio)MethodbasicconceptsandapproximationsparallelimplementationedgedislocationinSiMolecularDynamicsSimulationcarbonnanotubesMesoscopicSimulationself-assembly/self-organizationofquantumdotsquantumwiresOutline Experiment---Theory---ComputationTheoryNewtonianmechanicsStatisticalmechanicsQuantummechanicsComputationnanoscopicAtomisticElectronicExperiment AdvanceofComputerPower(FromF.F.Abraham) MissionToexplorethevariousmaterialspropertiesbycomputationalmodelingandsimulationPhysicalmodel+algorithmmaterialsproperties ObjectiveNotonlytoelucidateexistingexperimentalresultsbutalsotopredictnewmaterialsandnovelmaterialspropertiestobeexploredbyexperimentsETC Self-assemblyandself-organizationofNanostructures(quantumdotsandquantumwires)Nanofabrication:MechanicalpropertiesofnanoscalethinfilmsandofcarbonnanotubesNanomechanics/nanomechanicalarchitecture:Computationaldesigningofnanoscalethin-filmandCNTdevices(sensors,switches,…)Nanoelectronics:First-principlessimulationofAFMandSTMimagingNanoimaging:NanoclusterengineeringofcatalyticsurfacesNanocatalysis:Current&Near-FutureResearchTopics ComputationalSoftware(theory/modeling/simulationpackages)First-principlesandempiricalelectronicandatomicsimulationsofstructural,dynamic,mechanical,electronic,transportandmagneticpropertiesofnanomaterialsandnanodevicesNanoscopicsimulationsofgrowthandformationofthinfilmsandnanostructuresandself-assembly/self-organizationofquantumwiresandquantumdotsAnalyticaltheoryandcontinuummodelofnanostructuresandnanomechanics ComputationalHardware(in-houseBeowulfclusters)I/ORouterSimple-Construction---Cost-effective---Expandable VISCOComputationalInterface(VisualInteractiveScientificcomputing)VISCOWeb-BasedvisualizationinterfacecomputingResearch/EducationApplications:Provideaweb-basedvisualandinteractiveplatformforcomputationProvideacomputationalserverforabroadrangeofusers,(expertsornon-experts)Goscience,engineering,andbeyond SimulationatDifferentLengthScalesE=E({Ri})fi=dE/dRi(short-range)Equationofmotionofatoms{Ri}AtomicE=E({Li})fi=dE/dLi(long-range)Equationofmotionofboundaries{Li}Mesoscopic ComplexitiesofInteratomicPotentialsAbInitio(First-principles)Methods:Etot=Eele-ele+Eele-ion+Eion-ionInput:atomicspeciesSemi-Empirical(Classical)Methods:Etot=V2(R1-R2)+V3(R1,R2,R3)+…Input:potentialparameters ComparisonofAtomicSimulationMethodsmethodabinitioempiricalmechanicsquantumclassicalelectroniceffectyesno/approximateaccuracygoodfairefficiencyfairgood(systemsize)(10-103)(102-108) SimulationofMaterialsPropertiesEnergetics:cohesiveenergy,bondingenergy...StructuralProperties:crystalstructure,bondingconfiguration...ElasticProperties:modulus,elasticconstants,straindistribution...ElectronicProperties:bandstructure,chargedensity…DynamicProperties:latticedynamics,phasetransition... SimulationofDifferentMaterialsSystemsPointandExtendedDefectsThinFilms,Surfaces,andInterfacesMoleculesandClustersBulkMaterials CombineSimulationsatDifferentLengthScalesThermodynamicSimulationKineticSimulationMechanicalSimulationAbInitioBondingEnergiesDiffusionBarriersElasticConstants MultiscaleSimulationContinuumClassicalAbinito EdgeDislocationsinSiAlarge-ScaleAbInitioAtomicSimulationbyparallelcomputing PseudopotentialTotal-EnergyMethodDensityFunctionalTheory:modelelectron---electroninteractionPseudopotentialTheory:modelelectron---ioninteractionSupercellTechnique:modelsystemswithaperiodicgeometryIterativeMinimizationTechnique:optimizeelectroniccoordinates!ParallelImplementation! DensityFunctionalTheoryInteractingmany-electronproblemSingleelectroninaneffectivepotential1.HohenbergP.andKohnW.,Phy.Rev.136,864B(1964).2.KohnW.andShamL.J.,Phy.Rev.140,1133A(1965)Kohn-ShamEquation:Localdensityapproximation:Structuralparameters:atenthofanÅTotalenergydifference:afewpercentCohesiveenergy:>10% SupercellTechniquePeriodicboundaryconditionPlane-wavebasisexpansion AllelectronValenceelectronStrongionicpotentialWeakpseudopotentialPseudopotentialTheoryrpsVpsyaeyrZ Matrixdiagonalizationcpu~Np3IterativeMinimizationConventionalapproach:1.CarR.andParrinelloM.,Phy.Rev.Lett.55,2471(1985)Matrixmultiplicationcpu~Nb2NpIterativeapproach: ParallelImplementationPlane-waverepresentation:1.Clarke,Stich,andPayne,Comp.Phys.Comm.72,14(1992)Distributingthecomplexarray: ComputationalTechnicalDetailsLocalDensityApproximation:Ceperley-AlderformforexchangeandcorrelationPseudopotential:Kerker’snorm-conservingpseudopotentialSupercell:Plane-waveenergycutoffof8ryd.Twospecialk-pointstosampleBrillouinzoneIterativeMinimization:Preconditionedconjugate-gradientmethodParallelComputing:128nodesonIntelParagon ParallelSupercomputer+AdvancedAlgorithmLarge-ScaleAbInitioModelingandSimulation1.90opartialdislocation,Biggeretal,PRL,69,2224(92).2.ScrewDislocation,AriasandJoannopoulos,PRL,73,680(1994) MotivationTocarryoutalarge-scaleabinitiocalculationofedgedislocationsinSi,usingparallelcomputingElasticPropertiesElectronicPropertiesMechanicalBehaviorDevicePerformance (a/2)[110]EdgeDislocationinSiXTEM(M.Chisholm)ball-n-stickmodel-[110]projection ModelSystem:a/2<110>edgedislocation[110]projectionofdiamondSilattice- DislocationCoreFormation:iif Supercell:Dislocationdipole[110]projectionofa128-atomunitcell- StrainEnergy:periodiclatticesummationd2duvEc~coreenergycoefficient,rc~coreradiusb(r)~Burgersvector,K~elasticconstant, Properties:corestructure,coreenergy,strainfield,interactionenergy,electronicstructureSystemSizes:64atoms128atoms256atoms400atoms576atoms64atoms256atoms576atoms CoreStructure:MaximumDeviationinBondLengthNo.ofringsofseparationD% CoreStructure:MaximumDeviationinBondAngleNo.ofringsofseparationD% StressintheCore:MaximumAtomicLevelStressNo.ofringsofseparationsii(eV/Å3) DislocationStrainEnergyEc=0.75eV/Å,rc=4.1Å ElectronicStructureZXYKzKyKx400atoms576atoms64atoms128atoms1002000.10.20 StrainFieldandImpuritySegregation SummaryofDislocationSimulationCorestructure:nodanglingbondsorover-coordinatedSi,butlargedeviationinbondlength(8%)andinbondangle(20%)Abinitiovalueofcoreenergy:Ec=0.75eV/Å,rc=4.1ÅStrainenergy:exhibitalogarithmicdependenceondipoleseparation,consistentwithlinearelastictheory,downto~7Å.Electronicstructure:localizeddefectstatepenetratesintothegap~0.2eV.Strainfield:controlstheimpuritysegregationinthecore AcknowledgementTheory:V.MilmanM.MostollerT.KaplanExperiment:M.ChisholmSupport:DOE'