TosetupaworkfunctioncalculationEitherimportastructureofthebulkmaterialfromapre-existingfileorconstructanewstructureusingthesketchingandcrystalbuildingtoolsintheMaterialsVisualizer.GeometryoptimizethebulkstructureusingCASTEP.CleavetherequiredcrystallographicsurfaceusingtheCleaveSurfacedialogsothatthethicknessprovidesameaningfulrepresentationofthebulk.BuildavacuumslabusingtheBuildVacuumSlabCrystaldialog,youshouldensurethatthedistancebetweenthesurfaceandtheendofthevacuumisgreatenoughthattherecanbenopotentialinteractionsbetweenthesurfaceandthenextlayer.ChooseModules|CASTEP|Calculationfromthemenubar.SelecttheSetuptab.ChoosetheGeometryOptimizationtask.FixCartesianatomicpositionsofsomeatomsinthemiddleoftheslabusingtheEditConstraintsdialog,accessiblefromtheModifymenu.SelecteithertheLDAorGGAFunctionalfromthedropdownlist(seethetheorysectionformoreinformationonfunctionals).ClicktheRunbutton.FollowthestepsintheDisplayingtheaveragedpotentialchartforworkfunctioncalculationstopic.功函數(shù)計(jì)算1。輸入一個(gè)軟件自帶的已知體結(jié)構(gòu)，或用sketching

和crystalbuilding

工具建立一個(gè)新結(jié)構(gòu)。GeometryoptimizethebulkstructureusingCASTEP.CleavetherequiredcrystallographicsurfaceusingtheCleaveSurfacedialogsothatthethicknessprovidesameaningfulrepresentationofthebulk.BuildavacuumslabusingtheBuildVacuumSlabCrystaldialog,youshouldensurethatthedistancebetweenthesurfaceandtheendofthevacuumisgreatenoughthattherecanbenopotentialinteractionsbetweenthesurfaceandthenextlayer.ChooseModules|CASTEP|Calculationfromthemenubar.SelecttheSetuptab.ChoosetheGeometryOptimizationtask.FixCartesianatomicpositionsofsomeatomsinthemiddleoftheslabusingtheEditConstraintsdialog,accessiblefromtheModifymenu.SelecteithertheLDAorGGAFunctionalfromthedropdownlist(seethetheorysectionformoreinformationonfunctionals).ClicktheRunbutton.FollowthestepsintheDisplayingtheaveragedpotentialchartforworkfunctioncalculationstopic.功函數(shù)的計(jì)算一、熱電子發(fā)射和功函數(shù)A：常數(shù)W：功函數(shù)(或脫出功)，將固體中的電子移至其表面、并處于自由狀態(tài)所需的最低能量。V0EF0xVW金屬真空熱電子發(fā)射的電流密度為——Richardson定律V0：真空能級(jí)（勢(shì)阱的深度）W:2~6eV。此值與晶體方向有關(guān)，變化范圍約1eV。二.功函數(shù)的計(jì)算模型

構(gòu)造如右圖所示的2維無(wú)限陣列，計(jì)算的材料就是圖中的板，板間是真空層。用CASTEP計(jì)算此體系的EF和板間的靜電勢(shì)分布(r)，在平行表面的方向上對(duì)靜電勢(shì)取平均，從而在板間得到V0，進(jìn)而得到W。由于功函數(shù)W的數(shù)值依賴于晶體結(jié)構(gòu)和晶面取向，所以計(jì)算時(shí)需先優(yōu)化體材料的晶體結(jié)構(gòu)，再繪制2維陣列?？梢詢?yōu)化塊層表面和塊層內(nèi)部的原子坐標(biāo)，也可以不優(yōu)化。通過(guò)這些選擇，人們可以研究表面弛豫對(duì)功0.8-1nm3nm......slab函數(shù)的影響。一般建議利用constraints，固定塊層中間的原子，使其保留體材料的結(jié)構(gòu)。

對(duì)塊層進(jìn)行計(jì)算時(shí)，為了反映體材料的性質(zhì)，塊層的厚度至少在0.8-1nm。為了避免塊層相鄰表面間靜電勢(shì)的相互干擾，并使靜電勢(shì)達(dá)到其漸進(jìn)值，真空層的厚度至少為3nm。計(jì)算思路：對(duì)一定的晶體結(jié)構(gòu)，求出總電子能量最低的電荷密度分布(x’)，再根據(jù)右式計(jì)算位置x處的電勢(shì)(x)。顯示成球棒結(jié)構(gòu)轉(zhuǎn)化為原胞性質(zhì)不選優(yōu)化成功Saveproject,closeall打開(kāi)優(yōu)化后的W恢復(fù)為晶胞，準(zhǔn)備切面其它不變，改厚度至9埃切出一個(gè)厚度約9埃的表面。足夠厚，表示體性