Theory and Analysis of XAFS

《Theory and Analysis of XAFS》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。

1、Chapter2TheoryandAnalysisofXAFSJohnJ.Rehr,JoshuaJ.Kas,FernandoD.Vila,andMatthewNewville2.1TheoryofEXAFS2.1.1IntroductionOwingtoitselementspecificandshort-rangenature,core-levelX-rayabsorptionspectroscopy(XAS)isnowroutinelyusedtoelucidatethelocalstructural,vibra-tional,andotherphysicalpropertiesofco

2、mplex,aperiodicmaterials.XASencom-passesbothextendedX-rayabsorptionfinestructure(EXAFS)andX-rayabsorptionnearedgespectra(XANES)[1,2],wherethetermsrefer,respectively,tothestructureintheX-rayabsorptionspectrumμωðÞathighandlowenergiesrelativetotheabsorptionedgewiththecrossovertypicallyatabout20–30eVab

3、ovetheedge.TheacronymXAFSreferstothefinestructureatallenergies.Theextraordinarycapabilitiesofthesespectroscopiescomeataprice:theydependoncomparisonswithquantitativesimulationsofthespectra.Remarkably,however,theoriesofX-rayspectrahavebecomeincreasinglyaccurateandsophisticated,generallyovercomingthis

4、limitation[2–5].J.J.Rehr(*)•J.J.Kas•F.D.VilaDepartmentofPhysics,UniversityofWashington,Seatle,WA,USAe-mail:jjr@u.washington.eduM.NewvilleUniversityofChicago,ConsortiumofAdvancedRadiationSciences,AdvancedPhotonSource,GSECARS,Argonne,IL,USAe-mail:newville@cars.uchicago.edu©SpringerInternationalPubli

5、shingSwitzerland201713Y.Iwasawaetal.(eds.),XAFSTechniquesforCatalysts,Nanomaterials,andSurfaces,DOI10.1007/978-3-319-43866-5_214J.J.Rehretal.Formally,thetheoryofXASisbasedonFermi’sgoldenruleX2μωðÞjjhi0jjDFδωðÞþE0EF;ð2:1ÞFwhichrequiresasummationoverexactmany-bodyfinalstatesjiF,withenergiesEF.Howev

6、er,practicalcalculationsdependonthereductionofthisrelationtoaneffective,independentparticletheorythattakesintoaccountseveralimportantmany-bodyeffects.Thetheoreticaladvancesinrecentyearsaretheresultofanimprovedunderstandingoftheseeffectsandaccuratenewapproximations,inparticularforinelasticlossesand

7、vibrationaldamping[6].Thesedevelopmentsrelyonphysicsbeyondtheusualindependent-particleapproachesofquantumchemistryandcondensedmattersuchasHartree–Fockordensityfunctionaltheory(DFT).Moreover,theyinvolvedifferentli