粉末X射线衍射结构精修-贺蒙

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1、第十二届全国X-射线衍射学术大会暨国际衍射数据中心（ICDD）研讨会X射线衍射结构分析培训班粉末X射线衍射结构精修贺蒙国家纳米科学中心2010-10-26，绵阳概要•何为结构精修？•为何要做结构精修？•如何实现结构精修？•粉末衍射VS单晶衍射•Rietveld结构精修•如何利用Fulprof做Rietveld结构精修•典型应用何为结构精修？•调整晶体结构模型使其与观测到的实验数据最为符合的过程初始结构模型最终结构模型为何需要做结构精修？•使结构模型与实验观测数据最为符合！•隐含的逻辑：与实验观测数据最相符合的结构模型是最合理，最接近真实的结构模型。•在结构精

2、修过程中，完善结构模型，提高模型的质量，从而揭示更多有用信息。如何实现结构精修？

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10、2=f(a,b,c,,,,f,x,y,z,……)iiii2=??{

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14、2}2?=1???,???结构精修2最小化！Non-linearleastsquares:Gauss-Newtonalgorithm!LeastsquaresDataSet:i=1,...,nModelFunction:Residual:SquaredResiduals:NecessaryconditionsforminimumS:No

15、n-LinerleastsquaresIterativeProcess:粉末衍射vs单晶衍射粉末衍射vs单晶衍射TheRietveldMethodAminoffPrize,Stockholm,1995:"Inrecognitionofhisdevelopmentofprofilerefinementmethodsfortheanalysisofpowderdiffractiondata."TheRietveldMethodTheRietveldMethodconsistsinrefiningacrystal(and/ormagnetic)structureb

16、yminimizingtheweightedsquareddifferencebetweentheobservedandthecalculatedpatternagainsttheparametervector:n22wyiiyci()i1w1i2i2:isthevarianceofthe"observation"yiiLeastsquares:alocaloptimizationmethod•Theleastsquaresprocedureprovides(whenitconverges)thevalueoftheparameter

17、sconstitutingthelocalminimumclosesttothestartingpoint•Asetofgoodstartingvaluesforallparametersisneeded•IftheinitialmodelisbadforsomereasonstheLSQprocedurewillnotconverge,itmaydiverge.SoftwarefortheRietveldRefinementRietveldandmore…ParametersinPCRfileTheparametersinPCRfilecanbedivid

18、edintothreecategories-relatingonlytosamples,refinablesuchasatomicpositions,temperaturefactors-relatingbothtosamplesandinstrumentssuchasscalefactors,FWHM(Fullwidthathalfmaximum)-user-specifiedparameterssuchasBKPOS,NbaCodewords(I)codewordsareusedtocontrolparameterswhentoberefined,whe

19、ntobefixedandwhentobeconstrainedandetc.AcodewordisformedasC=S(10P+CC)WhereSstandsforthesignmark,Pisanordinalnumbersetbyusersfrom1top,themaximumnumberofparametersCodeword(II)•Forexample,anatomCapositionis(0,0,z)withztoberefinedfromitsinitialvalue0.1.ThecodewordinyourPCRfilelookslik

20、ethefollowing……Ca1Ca+20.00