B3LYP Explained - Chemistry Stack Exchange

B3lyp is a functional, that includes exact exchange and GGA corrections in addition to LDA electron-electron and electron-nuclei energy. The ... ChemistryStackExchangeisaquestionandanswersiteforscientists,academics,teachers,andstudentsinthefieldofchemistry.Itonlytakesaminutetosignup. Signuptojointhiscommunity Anybodycanaskaquestion Anybodycananswer Thebestanswersarevotedupandrisetothetop Home Public Questions Tags Users Unanswered Teams StackOverflowforTeams –Collaborateandshareknowledgewithaprivategroup. CreateafreeTeam WhatisTeams? Teams CreatefreeTeam Teams Q&Aforwork Connectandshareknowledgewithinasinglelocationthatisstructuredandeasytosearch. Learnmore B3LYPExplained AskQuestion Asked 5years,5monthsago Modified 5years,5monthsago Viewed 12ktimes 10 4 $\begingroup$ Inmyinorganicchemistryclass,wewereintroducedtocomputationalchemistry.WearetoldtouseB3LYPtheoryintheprogram,butweneveractuallylearnedanyofthecomputationyet.CouldanyoneexplainsimplywhatB3LYPisandhowitfitsintotheDFTequationthatlookslike $$ E_{\text{DFT}}[\rho]=T_{e}[\rho]+V_{ne}[\rho]+J[\rho]+E_{xc}[\rho] $$ computational-chemistrydensity-functional-theory Share Improvethisquestion Follow editedNov1,2016at1:31 pentavalentcarbon 7,23366goldbadges4343silverbadges7474bronzebadges askedOct21,2016at19:21 DrJessopDrJessop 21311goldbadge22silverbadges66bronzebadges $\endgroup$ 3 5 $\begingroup$ Uh,Ithinkyoushouldgrabatutorialorsomething.This'sgottobetoobroad. $\endgroup$ – M.A.R. Oct21,2016at19:32 1 $\begingroup$ B3LYPgivesyouanexpressionfortheexchange-correlationfunctionalintheDFTenergyequation.Forafewmoredetailsthismightbeofinterestforyou. $\endgroup$ – Philipp Oct21,2016at20:14 2 $\begingroup$ Idon'treallythinkit'stoobroad.It'squitepossibletogivearelativelyshortanswerexplainingwhatanexchange-correlationfunctionalis,pointingoutthatitreferstothelastterminthatequationabove,andtalkingalittlebitaboutB3LYPitself. $\endgroup$ – orthocresol ♦ Oct21,2016at20:58 Addacomment  |  1Answer 1 Sortedby: Resettodefault Highestscore(default) Datemodified(newestfirst) Datecreated(oldestfirst) 12 $\begingroup$ 'Theleveloftheory'isafancywordforschemeusedtocalculateenergyofamolecule.Therearequitemanywaystodoit,mostverycomputationallyexpensive.However,quiterecentlyitwasproventhatstateenergydependsonelectrondensitydistributiononly,anddetailsofcorrelationofelectronmovementarederivablefromsaiddistributioninallentirety.Thisgaverisetodensityfunctionalmethods,whereinsteadofconsideringalldetailsofelectronmovement,onlyelectrondensityisconsidered.Theoreticallythisallowstolowercomputationalrequirementsfromfourth-seventh(dependsonthemethodused)powerofnumberofbasisfunctionstoonlythirdpowerofsaidnumber.Thisisabigdeal. Theproblemisthatexactanduniversalwaytoderiveenergyofasystemofelectronsfromtheirdistributionisunknown.Thus,alotofvariouswaysweretestedandmostsuccessfulonesmadeitintoavailablesoftware. Mostofsuchways-functionals-splitenergyofthesystemintoseveralparts.Someofthemmaybeknownexactly,suchasenergyofelectron-nucleuiinteraction.Some,however,arenot,suchasenergyofelectron-electroninteraction.Still,severalbordercaseswereconsideredintheoreticalphysics.Specifically,functionalforelectrongasisknownandwasused.ThisgaveraisetosoknownLocalDensityApproximation.Itperformstolerableinmanycases. Aninterestingoptionistoaddso-knownexactexchangeintothemix.Essencially,exactexchangeisanattempttoenforcePauliprinciplebyhand,i.e.thattwoelectronswithsamespincannotoccupythesamespot.Theproblemis,thatpartofitisalreadyincludedinthebaseLDA,sothatmemberisusuallyconsideredwithreducedweight,say,0.25. Anotherpossiblewayistotrytoincludemembersdependentonelectrondensitygradient,toaknowledgethatelectrondensityinamoleculevariesfrompointtopoint.ThisisknownasGGAapproach. B3lypisafunctional,thatincludesexactexchangeandGGAcorrectionsinadditiontoLDAelectron-electronandelectron-nucleienergy.Theweightsofthepartswerefittoreproducegeometryofatestsuiteofsmallmolecules.Assuchuseofb3lypforcalculationswithheavieratomsisquestionable. Densityfunctionalsperformpoorlywhendispersioninteractionsplaysignificantrole,thoughtcorrectionschemesforthisarealsoknown. Furtherdetailsarenotimportantforyouatthemoment.However,considergrabbingsomebookonDFTandquantumchemistryingeneral.Ifyoueverendin'real'chemistry,thiswouldcomehandy,ascomputationalchemistrypapersarepresentinbignumbersandoftenoffersignificantinsight. Share Improvethisanswer Follow editedOct21,2016at22:52 answeredOct21,2016at22:02 permeakrapermeakra 20.5k11goldbadge4848silverbadges9494bronzebadges $\endgroup$ Addacomment  |  YourAnswer ThanksforcontributingananswertoChemistryStackExchange!Pleasebesuretoanswerthequestion.Providedetailsandshareyourresearch!Butavoid…Askingforhelp,clarification,orrespondingtootheranswers.Makingstatementsbasedonopinion;backthemupwithreferencesorpersonalexperience.UseMathJaxtoformatequations.MathJaxreference.Tolearnmore,seeourtipsonwritinggreatanswers. Draftsaved Draftdiscarded Signuporlogin SignupusingGoogle SignupusingFacebook SignupusingEmailandPassword Submit Postasaguest Name Email Required,butnevershown PostYourAnswer Discard Byclicking“PostYourAnswer”,youagreetoourtermsofservice,privacypolicyandcookiepolicy Nottheansweryou'relookingfor?Browseotherquestionstaggedcomputational-chemistrydensity-functional-theoryoraskyourownquestion. 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