资源描述：
《月份基组的使用（use of base groups in november）》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、月份基组的使用（UseofbasegroupsinNovember）Ondiffusionfunctionandbasegroupof"month"Text/Sobereva2012-Jan-131whendoyouneeddiffusefunction?Thediffusionfunctioninquantumchemistrycalculationisaverysmallbasefunctionwithaverywidespatialdistribution.Dispersionfunctionsareimpor
2、tant,andevennecessary,formanyproblems,Including:thecalculationoftheweakinteraction,electronaffinity,I/multipolemomentsandpolarizability,opticalactivity,highorderreactionbarrier,excitedstate,oflonepairelectrons.Ifthesystemisananion,besuretohaveadiffusionfunction
3、.Ifonlysomeoftheatomsarenegativelychargedorpolarized,orweakinteractionsinvolveonlyonepartofthesystem,atleasttheatomsintheseregionsshouldbesmearedwithdiffusionfunctions.Whenthedispersionfunctionisneeded,inordertoaddthedispersionfunction,itisbettertoreducethezeta
4、number,forexample,whencalculatingtheweakinteraction,itisbettertodropfromthreezetatotwozeta,plusthediffusionfunction.Inothercases,dispersionfunctionsarelessimportant,andinordertosavecomputation,nodiffusionfunctioncanbeused.Suchasthecalculationofionizationpotenti
5、al,atomicenergy,valenceexcitedstates.Thedispersionfunctionisnotimportantiftheproblemdoesnotbelongtotheabovetype,andthesystemiscationic,orthesystemdoesnotcontainatomswithverylargenegativechargesandpolarizableatoms.2problemscausedbydispersionfunctionTheadditionof
6、diffusionfunctionsincreasesthecompletenessofthebasisfunctions.Intheory,itshouldalwaysbeusefulandharmlesstotheresults,butinpracticeitleadstothefollowingproblems:1,theamountofcomputingsoared.Thisiswellknown,especiallyifthecc-pVnZseriesisoftenaddedtotheaug-,evenif
7、itdoesn'tmove,thefourthsectionwilldiscusshowtosolvetheproblem.2,itisoftenmoredifficulttoconvergethanaddingnodiffusionfunctionafteraddingthediffusionfunction.3,theproblemoflineardependenceofbasisfunctionsleadstonumericalproblems.However,inthegeneralquantizationp
8、rocedure,theeigenvalueoftheoverlapmatrixofthebasisfunctionisautomaticallychecked,andsomebasefunctionsarecutoffproperlytosolvetheproblem.4,whencalculatingtheweakinteraction,t
