小木虫 --- 500万硕博科研人员喜爱的学术科研平台
&&查看话题
fix heat计算石墨烯热导率，固定两端原子是否合适？
大家好，我刚接触lammps，想采用fix heat方法计算石墨烯纳米带的热导率。我看很多文献上为了防止石墨烯纳米带的整体移动通常将纳米带两端的原子固定。但是我采用该方法进行计算后，发现在弛豫过程中，虽然体系整体的温度保持在400K，但是由于两端原子固定的原因导致温度分布出现中间高两端低的现象，如下图：
当体系达到平衡后，在体系的左端加入热量，右端抽取热量。由于固定原子的存在导致与其相邻的原子速度相对较低，因此如果抽取的热量过高时则会导致原子速度降低至零而出现错误。下面是我的in文件，希望了解的大神能帮我看一下，是否是我in文件中设置有问题，在此谢过了！！
# MD simulation of Graphene thermal conductivity
# Initialization
units& && && && & metal
variable& & & & & & T equal 400
variable& & & & & & V equal vol
variable& & & & dt equal 0.0005
variable& & p equal 10000& &&&# correlation length
variable& & s equal 1& && &# sample interval
variable& & d equal $p*$s& &# dump interval
variable& & width& &equal& &14.6544
variable& & kB equal 1.& & #&&Boltzmann
variable& & eV2J equal 1.602e-19
variable& & A2m equal 1.0e-10
variable& & ps2s equal 1.0e-12
variable& & convert equal ${eV2J}*${eV2J}/${ps2s}/${A2m}
dimension& && && &3
newton& && && && &on
boundary& && && & p& &p& &p
atom_style& && &&&full
neighbor& && && & 0.3& & bin
neigh_modify& && &check&&yes
lattice& && && &&&fcc& &1
region& && && && &box&&block 0.000& &14.& & 100.00&&0.000& & 50.000&&units lattice& &y方向为热流施加方向，为防止两端原子的相互作用将y方向盒子长度设置为10nm,并将石墨烯纳米带放置于盒子中部
read_data& & & && &graphene.data
################### set group ############################
region& && && && &up& & block&&INF INF&&INF 26.0&&INF INF&&units lattice
region& && && && &down&&block&&INF INF&&81&&INF&&INF INF&&units lattice
region& && && && &steady union 2&&up down
group& && && && & steady region steady& && && &
region& && && && &remain block&&INF INF 26.0&&81&&INF INF&&units lattice
group& && && && & remain region remain
region& && && && &hot& &block&&INF INF&&26.0 36.0&&INF INF&&units lattice
group& && && && & hot&&region&&hot
region& && && && &cold&&block&&INF INF&&71&&81&&INF INF&&units lattice
group& && && && & cold&&region&&cold
velocity& && && & remain&&create&&$T 458 mom yes&&dist gaussian units lattice
velocity& && && & steady&&set&&0.0 0.0 0.0
# Potential *********************************************************
pair_style& && &&&airebo 2.0&&
pair_coeff& & & && &*&&*& &CH.airebo&&C
fix& && && && && &nve&&remain&&nve
fix& && && && && &temp remain&&temp/berendsen $T $T 0.0005
fix& & & & & & & && &1 steady setforce 0.0 0.0 0.0
compute& && && &&&mytemp&&remain&&temp
compute& && && &&&hottemp hot& &&&temp
compute& && && &&&coldtemp cold& &temp
compute& && && &&&ke&&remain&&ke/atom
variable& && && & temp atom&&c_ke*${eV2J}/(1.5*${kB})
fix& && && && && &temp_profile1& & remain& & ave/spatial&&1&&00000&&y&&lower&&1.0& && &v_temp&&file&&11.profile& & units&&lattice
thermo_style& && &custom step c_mytemp c_hottemp c_coldtemp etotal vol
thermo_modify& &&&lost warn
thermo& && && && &500
timestep& && && & ${dt}
dump& & & & & & & && &1 all atom 1000 dump.lammps
run& && && && && &2000000
unfix& && && && & temp
fix& && && && && &hot& &remain&&heat&&1& &1& &region hot
fix& && && && && &cold&&remain&&heat&&1&&-1& &region cold
run& && && && && &2000000
reset_timestep& & & && &0
fix& && && && && &temp_profile2& & remain& & ave/spatial&&1&&00000&&y&&lower&&1.0& && &v_temp&&file&&temp.profile& & units&&lattice
dump& & & & & & & && &2 all atom 1000 graphene.lammps& &
& && && && &&&
run& && && && && &&&# every 1 set group steady vx 0 vy 0 vz 0
未施加温度梯度时的温度分布
很多计算热导率的文章都是采用周期边界条件，都没有固定原子，但是在热整流的模拟中，由于材料左右方向的不对称性，无法采用周期边界条件，因此都将两端原子固定了。
研究生必备与500万研究生在线互动！
扫描下载送金币
浏览器进程
打开微信扫一扫
随时随地聊科研君，已阅读到文档的结尾了呢~~
扫扫二维码，随身浏览文档
手机或平板扫扫即可继续访问
薄膜热导率的测试与分子动力学模拟研究
举报该文档为侵权文档。
举报该文档含有违规或不良信息。
反馈该文档无法正常浏览。
举报该文档为重复文档。
推荐理由：
将文档分享至：
分享完整地址
文档地址：
粘贴到BBS或博客
flash地址：
支持嵌入FLASH地址的网站使用
html代码：
&embed src='/DocinViewer-4.swf' width='100%' height='600' type=application/x-shockwave-flash ALLOWFULLSCREEN='true' ALLOWSCRIPTACCESS='always'&&/embed&
450px*300px480px*400px650px*490px
支持嵌入HTML代码的网站使用
您的内容已经提交成功
您所提交的内容需要审核后才能发布，请您等待！
3秒自动关闭窗口computedrange.Thethermal；Whencompressivestrainisa；sinusoidalfunction:z=Asi；?andAGNRandZGNR,thevalue；?and90.0A??forcompressiv；forcompressivestrainat?0；Inordertoelucidatethestr；κ=Cvv
computedrange.Thethermalconductivityreductionis60%(40%)inZGNR(AGNR),approachingthetensilefailurelimitof0.20(0.10).ThisisbecausethegeometryofAGNRismoresensitivetotensilestrainthanthatofZGNR,asseenin?gure3(b).AGNRhasalargerstressthanZGNRunderthesamecondition.CarbonCcarbonbondsareelongatedandanglesarechangedundertension.Inordertoanalyzetheresultsquantitatively,wecalculatedthecarbonCcarbonbondlengthsandanglesfromcompressivetotensilestrainwithevery0.01strainstepandtheobtainedvaluesareaveragedoverall.Wecanclearlyseethatthebondsalongthetensiledirection,bondtypeBforZGNRandbondtypeAforAGNR(see?gure1),undergomoredeformationandarethemajorfactorscausingstress.ThelargerdeformationofbondtypeAofAGNRisduetothesmallermagnitudeofbondanglevariationinthearmchairdirection,whichsuggeststhelargerstressofAGNR.Mechanicalpropertiesofbulkgraphenehavebeeninvestigatedusingexperimental[36,37]andtheoretical[38,39]methods.Ourresultsareconsistentwiththereportsfrom[40].ThermalconductivityofCNTsunderstrainisalsoillustratedforcomparison.ForCNTs,onlytwotypicalcasesoftensilestrainat0.02and0.05arecomputed.Theirthermalconductivityvaluesobtainedhereareconsistentwiththosereported[22].ThereductionofthermalconductivityofCNTsisgreaterthanthatofZGNRwhentheappliedstrainislessthan0.025,butlesswhenthetensilestraingoesbeyond0.025.AsfortheAGNRcase,thiscriterionis0.05.Reasonscouldbelinkedwiththemore?exiblestructureofGNRsundersmallstrains,whichwouldcontributetothesmallerreductionofthermalconductivity.Whenthetensilestrainislarge,phononscatteringandinstabilityattheGNRedgesbecomedominant,whichleadstothereductionofheattransferandthereforethedramaticdecreaseofthermalconductivity.WecanseethatGNRshaveamuchwidertunablerangeofthermalconductivity((1.0C0.6)forAGNRor(1.0C0.4)forZGNR)thanthatofCNTs(1.0C0.63).
Whencompressivestrainisapplied,thethermalconductivityofGNRs,bothAGNRandZGNR,exhibitsthesametrendofchange.Asmallreductionofthermalconductivity(lessthan10%)ofGNRsisobtainedatstrain?0.10,whichisdifferentfromthetraditionalbulkmaterial[19]whosethermalconductivityincreasesundercompression.ReasonsshouldbeplacedatthefocusofGNR’suniquestructure.GNR’s2Datomicmonolayerstructurecanformcorrugationsthatcouldreleasethestressbytransversede?ection,asshownintheinsetof?gure3(b).ThestressofGNRs(AGNRandZGNR)isalmostzeroundercompression.FurtherinvestigationofthevariationofcarbonCcarbonbondlengthsandanglesinGNRsundercompressionrevealsthatthecompressivestrainshavenotchangedthecarbonCcarboninteratomicmicrostructure.However,thecorrugationinducedbycompressionandtheincreaseofedgeinstabilityresultinunfavorablepropagatingphononsandareresponsibleforthereductionofthermalconductivity.ThecorrugationshapeofGNRs(AGNRandZGNR)intheXZplanecanbe?ttedintoa
sinusoidalfunction:z=Asin2λx,where,xandzaretheatoms’coordinatesoftheGNRinthexandzdimensions,respectively,Aisamplitudeandλiswavelength.Forboth
?andAGNRandZGNR,thevaluesofAandλare7.07A
?and90.0A??forcompressivestrainat?0.05,9.93A95.0A
forcompressivestrainat?0.10,respectively.Lietal[11]reportedthatthethermalconductivityofgraphenedecreasesremarkablyundercompressionbecausetheyperformedstrainsintheplane(XandYdirectionsasillustratedin?gure1),whichcausebucklingforthesingleatomicmonolayernatureofthegraphenesheetstructure.Similarresultswereobtainedinourexercises.Furthermore,theCNTthermalconductivityismoresensitivetothecompressivestrainthanthatofGNR,asseenin?gure3(a).Thisisbecausethebending(atsmallcompressivestrain)orbuckling(atlargecompressivestrain)deformationresultsintheincreaseofphononscatteringandthusreducesthermalconductivity.
Inordertoelucidatethestraineffectonthermaltransportproperties,weinvestigatethevariationofphononspectraofZGNRandAGNRunderdifferentstrains(see?gure4(a)and(b)).ThephononspectrumfunctionG(ω)iscalculatedfromtheFouriertransformofthevelocityautocorrelationfunction(VACF)mentionedabove.TheFouriertransformoftheVACFisthepowerspectrum,theamountofenergyinvibrationsateachfrequency,whichisproportionaltothephonondensityofstatestimestheoccupationofthemodes.Asshownin?gure4(a)and(b),undercompressivestrain,thephononspectraofZGNRorAGNRarealmostinvariable,whereastensilestrainswouldsoftenthehigherfrequencypeaks(Gband)ofthephononspectraremarkably,whichcouldslowdownthephonongroupvelocitiesandresultinathermalconductivitydecreaseaccordingtotheclassicallatticethermaltransporttheory:??
κ=Cvvml(8)
wheremisthephononmodeoccupiedataspeci?c
Cv,vmandlarethespeci?cheat,groupvelocityandmeanfreepathofthephonon,respectively.Differentfrom3Dconventionalmaterial,whosephononspectratranslategloballyunderstrain,higherfrequencyphononsplayamuchmoreimportantroleinGNRsunderstrain.ThelocationsofGbandsare?ttedbyaGaussianfunction,andtheirrelationshipwithstrainsandthermalconductivityareillustratedin?gure4(c)and(d).Wecanseethat,comparedtoZGNR,AGNRismore?exibleundercompressionfortheirmorestablephononspectra,whileitismoresensitivetotensionwithaslightlyfasterredshiftoffrequency.In?gure4(d),wepresentthethermalconductivityofZGNRandAGNRasafunctionofG-bandfrequenciesandtheirtrendlinesarealmostconsistentwitheachother,whichisslightlydifferentfromthetrendofthermalconductivityversusstrain.
Thatisduetothede?nitionofstrainε=l?l0,wherel0istheoriginallengthandlisthe?nallength.Thecontributionstoelongation(l?l0)comefromthestretchingofthebondandtheincrease/decreaseofbondangle(see?gure3(c)and(d)).TheircontributionstostrainaredifferentinAGNRandZGNRfortheirdifferentgeometrystructuresandarenotequivalenttothecaseofthermalproperties.Inpractice,thestretchingofbondshasmoreeffectontheshiftofphononspectra.Inaddition,theshiftofphononspectrare?ectstheintrinsicstrain
Figure4.(a)and(b)arethephonondensityofstates(PDOS)asafunctionoffrequencywithstrainsfrom?0.10to0.20for10-ZGNRandfrom?0.10to0.10for19-AGNR.Phononfrequencyasafunctionofstrainandthermalconductivityisshownin(c)and(d).Therelationofthermalconductivityandfrequencyis?ttedusingPeierlsCBoltzmannformulations[19],(equation(9)),shownas‘Fitting1’,aswellasapolynomial?ttingformula(κ/κ0=a0+a1(ω/ω0)+a2(ω/ω0)2+a3(ω/ω0)3+a4(ω/ω0)4+a5(ω/ω0)5)(labeledas‘Fitting2’),wherea0==?,a2=,a3=?,a4=anda5=?39903.40.
effectonthermalpropertiesinvolvedincontributionsfromthestretchingofthebondandvariationofbondangle.
3Dtraditionalmaterialsshowapower-lawscalingofthermalconductivityonphononfrequencyderivedbyBhowmicketal[19],whichcanbededucedfromthePeierlsCBoltzmannformulation.Therelationofthermalconductivityversusphononfrequencyis
whereωandω0arethephononfrequencieswithandwithoutstrains,respectively.γisapotential-dependentexponent.αistheGr¨uneisenparameterwhichisalsopotential-dependent.Thispower-lawcandescribewellthephonefrequencydependenceofthermalconductivityofGNRatlargestrains,butnotatsmallstains,asinourcase(?gure4(d)).ThisisbecauseoftheuniquestructureofGNRthathassomeintrinsiccorrugationsatzeroorslightstrains,whichcouldreducethestraineffects.Apolynomial?ttingformulaisfoundtocloselyresemblethefeatureofthiscurve.Thephononfrequencydependenceofthermalconductivityinlow-dimensionalmaterialisoneoftheongoingsubjects.
Inadditiontouniaxialstrains,wealsopresentin?gure5thestructuresofagraphenesheetundervariousbiaxialstrains(in-planestrainsinXandYdirections).Graphenehassomeripplesorcorrugationsinafreestandingsheet[40],whichisalsoclearlyfoundinoursimulationofasquaregraphenewithasizeof10.0×10.0nm2usingperiodicconditionsinbothXandYdirections,asshownin?gure5(c).Itclearlyshowsthat
Figure5.Structuresofsquaregrapheneunderin-plane(XandYdirections)strainsandappliedstraindirectionsarelabeledwithlightbluearrows.Asin?gure1,heat?uxisperformedalongtheXdirection.(a)CompressivestrainsareappliedinbothXandYdirections.Graphenewillformbucklingandstrongcorrugation.
(b)Compressivestrainisappliedinthethermaltransferdirectionandgraphenewillbecomeanarch-likestructure.(c)Squaregrapheneinabsenceofstrainasareference.(d)Compressivestrainisappliedinperpendiculartothermaltransferdirection(Ydirection).(e)TensilestrainsareappliedonthegrapheneinbothXandYdirections.Grapheneis?attenedundertensilestrains.
graphenesheetbuckleswhencompressivestrainsareappliedinbothXandYdirections(see?gure5(a)).WhencompressivestrainisappliedintheXorYdirectionsonly(?gure5(b)or(d)),agraphenesheetwillformanarch-likestructure,whereas
Figure6.(a)Thermalconductivity(κ)ofsquaregraphene
(10.0×10.0nm2)asafunctionofstrainintheYdirectionwith?xedstrainsintheXdirectionat?0.10,0.0and0.10(whicharelabeledwithbluetriangle,redsquareandblackdot,respectively)underperiodicboundaryconditions.κ0isthethermalconductivityof
graphenewithzerostrainintheYdirection,anditsvaluesare92.86,102.07and54.45WmK?1forXstrainsat?0.10,0.0and0.10,respectively.(b)StressCstrainrelationofsquaregraphenewithinitialstrain?0.10,0.0and0.10intheYdirectionat300K.
agraphenesheetwillbe?attenedunderin-planetensilestrains.Itisinterestingtostudybiaxialstraineffectsonthethermalconductivityofgraphenewhichhasanadditionaldimensionto
control.Effectsofstrainalongthethermaltransferdirectiononthermalconductivityarewellstudiedasmentionedbefore.Wenowdiscusstheeffectsofstrainsperpendiculartothethermaltransferdirectiononthermalconductivityofgraphene,atypicalcasethatremainsunexplored.Insuchasimulation,thermalconductivityofgrapheneisstudiedwitha?xedstrain(?0.10,0.0and0.10)intheXdirection(i.e.thermaltransferdirection)andunderstrainloadedfrom?0.08to0.08intheYdirection(namely,perpendiculartothethermaltransferdirection).Figure6(a)plotsthermalconductivityasafunctionofstrainintheYdirection.Whenthe?xedstraininXis?0.01,thethermalconductivitydecreaseswhencompressiveortensilestrainsareappliedintheYdirection,andthusthepeakthermalconductivityoccursatzerostrainintheYdirection.Suchatendencyisconsistentwithaprevioustheoreticalreport[11].Thatisbecausethegraphenesheetwillformabucklingstructureunderbiaxialcompressivestrain,asshownin?gure5(a),whichcanincreasephononscatteringandthusdecreasethermalconductivityaccordingly.WhenthereiszerostraininX,itisworthnotingthatthermalconductivityincreasedwithsmallstrains(upto±0.04),inwhichcasebothcompressiveandtensilestrainswereappliedperpendiculartothethermaltransferdirection.Toexplaintheincreaseofthermalconductivityofgrapheneunderslightperpendicularstrains,weanalyzethedisplacementofcarbonatomsonthesurfaceofthesheetwithstrainsat?0.04,0.0and0.04intheYdirection,respectively,asshownin?gure7.Wecanseethataslightstrain,eithertensileorcompressivestrainsperpendiculartothethermaltransferdirection,cansmooththegraphenesheetandthusincreasesthermalconductivity.ThermalconductivitywilldecreasewithfurtherincreasedstrainintheYdirectionduetotheincreaseofthelatticeinstability.
Whenthe?xedappliedstrainis0.10intheXdirection,thermalconductivitydecreasescontinuouslyfromzerostraintotensilestrain(0.08)appliedintheYdirection,similartothecasesofGNRs,CNTsandbulkmaterials[11].However,interestinglyenough,theresponseofthermalconductivityofagraphenesheetwithcompressivestrainsappliedinthe
Figure7.Distributionofdisplacementofatomsofsquaregrapheneat300Kwithcompressivestrain?0.04(a),zerostrain(b)andtensilestrain0.04(c)intheXdirection.
Figure8.(a)C(c)Variationofbondlengthofgrapheneasafunctionofstrain.Thede?nitionsofbondtype‘bondA’and‘bondB’arethesameasforZGNRin?gure1(a).(d)C(f)Theevolutionofbondanglesgrapheneunderstrain.Similarly,‘angleα’and‘angleβ’arede?nedin?gure1(a).
directiontogetherwitha?xed0.10tensilestrainintheXdirectionclearlyshowsdifferentbehaviorcomparedtocaseswithothercombinedco-axialstrains.ThethermalconductivityincreasesdramaticallywhencompressivestrainsintheYdirectionexceed?0.04,asclearlyillustratedin?gure6(a).
Weplotin?gure6(b)thestressCstrainrelationsofgrapheneunderin-planestrains(XandYdirection).ItclearlyshowsthatagraphenesheetbecomesstiffintheYdirectionwhenthegrapheneisunderacompressivestrainintheXdirection.Ontheotherhand,graphenewillbecomesoftintheYdirectionwhenitisunderatensilestrainintheXdirection.Thatisbecauseagraphenesheetwillbuckleunderin-planecompression(bothXandYdirections),whichneedsmoreenergythanformingwave-likeorarch-likestructures.WhengrapheneisunderstretchingintheXdirection,carbonCcarbonbondlengthsareelongatedalongtheXdirectionandinteractionsamongcarbonatomsbecomeweaker,asshownin?gure3(b),andthussoftengraphene.
VariationsofbondlengthandbondangleofgraphenearestudiedunderbiaxialstrainswithdifferentratiosintheXandYdirections.Thede?nitionofbondandangletypesarethe
sameasforZGNR(see?gure1(a)).Ascanbeseenin?gure8,forthecaseswithcompressive(?0.1)orzerostrainsappliedintheXdirection,bondlengthsandanglesofGNRsarealmostinvariableundercompressionintheYdirection(?gure8(a),(b),(d)and(e)),eveninthecaseofbuckling(?gure8(a)),becausethestructureofsingle-atomic-layergraphenemakesiteasytoreleasethecompressivestrainbytransversede?ection.However,thebondlengthsandanglesofGNRsarequitesensitivetothetensilestrainsintheYdirection,asillustratedin?gure8(a),(b),(d)and(e).Whengrapheneisundera?xedtensilestrainof0.10inX,bothbondlengthandangledeviated
?awayfromthepositionswithoutstrains(approximately1.40A
and120?forbondlengthandangle,respectively).Fromtensilestrain(0.08)tocompressivestrain(?0.08)inY,thebondlengthdecreasescontinuously,approachingconstantvalues,
?forbondAand1.42A?forbondB.Thetwonamely1.48A
bondangles(α,βin?gure8(f))divergedwhenthestraininYchangedfromtensiletocompressive.Suchdifferentstructuralresponsestodifferentappliedstrainsprovidethephysicalinsightforthemechanismofitsrichthermaltransportbehavioringraphenesheets.Inparticular,theanomalousevolution
Figure9.Twisted10-ZGNRsfrom1to3πbefore((a),(c),(e))andafter((b),(d),(f))structuraloptimizationusingthePolakCRibiereversionoftheconjugategradientalgorithm.Uponoptimization,the‘single-twisted’structurefor1πtorsionisalmostunchanged
((a)C(b)),the‘double-twisted’structurefor2πtorsiontransformstoapillaredstructure((c)C(d))and‘triple-twisted’structurefor3πtorsionbecomestube-likewithunevenlydistributeddiameters((e)C(f)).
3π,thestructureturnstube-likewithnon-uniformdistributed
?diameters,from3.0to4.6A.
Inordertounderstandthisissuemoreclearly,thermalconductivityof(5,5)CNT,whichisformedbytherollingof10-ZGNR,isalsocalthevalueoftheCNTisfoundhigherthanthethermalconductivityoftheparent10-ZGNR.ThisisbecausetheedgephononscatteringplaysanimportantroleinsuchasmallsheetofGNR.TheevolutionofZGNRundertorsion,fromnanoribbontotube-likestructure,canbeexaminedthroughbondlength,edgelengthandbondangle(see?gure10(b)C(c)).ThevariationsofedgelengtharestudiedfortheinhomogeneousstructureintwistedZGNR.Also,asshownin?gure10(d),thephononspectraofthetwistedGNRbecomeclosertoCNTsasthetorsionalangleincreases.
4.Conclusion
Inthispaper,straineffectsonthethermalconductivityofGNRswithdifferentedges(ZGNR,AGNR)havebeenstudiedsystematically.ThethermalconductivityofGNRsdecreasesremarkablyundertensilestrain.However,itisinsensitivetocompressivestrain.Thisintriguingphenomenonisexplainedbythe?exibletwo-dimensionalmicrostructureofgraphene,whichissupportedbythedetailedanalysesofcarbonCcarbonbondlengthandbondangleaswellasphononspectra,inacorrugatedstructureundercompression.Underslightstrains(&0.05),bothtensileandcompressivestrainsreducethethermalconductivityatthesamerate,butwithdifferentmechanisms.Undertensilestrain,thermalconductivityisreducedbysofteningthephononmodes,whileundercompressivestrainthephononmodesarealmostconstant.Fora2Dgraphenesheet,itwillformanarch-likestructurewithcompressivestrainappliedinonedirection,butitwillbe?attenedunderin-planetensilestrains.Whencombinationalstrainsareappliedinbothdirectionsparallelandperpendiculartothethermaltransferpath,2Dgraphenesheetshavecomplexreconstructionssuchasanisotropicbuckling-likeandarch-likestructures.Someofthestructurescanhavehigherthermalconductivitythanthatofafree-standinggraphenesheetwithoutstrain.Whenatorsionalstrainisapplied,GNRswill?rstlyformahelical-likenanostructureandthenturnintoatube-likenanostructurewhenstrainisincreased.Generallyspeaking,byapplyingstrain,thethermalconductivityofGNRscanbetunedinawiderrange,from1.0to0.4(1.0to0.6)forZGNR(AGNR)comparedtothatwithoutstrain.TunablethermalconductivityofGNRsusingtensilestraincanbeutilizedinthermalmanagementandsensorapplications.RobustnessofthethermalpropertiesofgraphenesheetsandGNRsundercompressiveandtorsionalstrainhasapplicationsinthermaldevicesforwhichhigherandmorestablethermalconductivityisdesirable.Inparticular,thetorsionalstrainshavebeenshowntotunetheelectronicpropertiesofCNTsreversibly[41].OurstudyonthermaltransportoftwistedGNRswithvarioustorsionalstrainsprovidesadditionalinsightintotheuniquethermalpropertiesofsuchinterestingnanostructureandshedssomelightonpotentialapplicationsoftwistedGNRs.Although9
ofbondlengthandbondanglewithtensilestraininXcanwellexplaintheunusualincreasingthermalconductivitywithincreasingcompressivestrainsintheYdirection(?gure6).
Atwistedgraphenenanoribbon(TGNR)isproducedbyapplyingapairofequaltwistingmomentsinoppositedirectionstotheshortsideoftheribbon.Thetotaltwistedangleinoneunitribbonmustbenπtomeetperiodicconditions,wherenisanintegernumber.Laterthestructuraloptimization[2]isperformedtoobtainthe?nalstructure.Figure9showshowtheGNRistwistedandpresentsthestructuresbefore(denotedas(a)structure)andafter(denotedas(b)structure)optimization
Thein?uenceoftorsionalstrainonthermalconductivityofGNRsisinvestigatedwhichshowsanewaspecttostudytheeffectofradialstress.Weonlystudiedthetwisted10-ZGNRof10.0nmlongforitsmore?exiblestructure.Thetwistedanglesrangefrom0to3π(largertwistangleswillresultinfailureundertorsionalstrain).TheanglerangeisdependentonthewidthandlengthoftheGNR.Generallyspeaking,narrowerandlongerGNRscanhavegloballylargertorsionalangleswithinthefailurelimit.
Similartocarbonnanotubes,thermalconductivitydecreaseswiththeincreaseoftwistedangle,asillustratedin?gure10(a).However,ZGNRwithopinsteaditformsatube-likestructureatatorsionalangleof2πandreducesthermalconductivitybyapproximately10%.Whenthetorsionalangleisincreasedto3π,thestructureturnstube-likewithunevenlydistributeddiametersandthethermalconductivitydropssigni?cantlybyabout40%,duetostrongphononinterfacescattering.WestudiedthevariationofradiusofTGNRwithvariouskindsoftorsionalangles(see?gure11).Thede?nitionoftheradiusofTGNRisthedistancebetweenXaxis(atthecenter)totheedgesoftheGNR.Whenthe
?implementedtorsionalangleis1π,theradiusiskeptat5.0A
whichisthesameasforuntwistedGNRalongtheXaxis.
?whenthetorsionalangleTheradiusreducestoabout3.0A
is2πandtheGNRbecomeatube-likestructure.However,thetube-likeGNRisstillhomogeneouswithinvariableradiialongtwistedaxis(Xaxis).Whenthetorsionalangleisincreasedto
包含各类专业文献、行业资料、生活休闲娱乐、应用写作文书、中学教育、文学作品欣赏、各类资格考试、专业论文、lammps计算石墨烯热传导45等内容。　
　对于多层石墨烯,其热导率低于单层石墨烯,且热导率随着层数的 增多而减小[11]...2. 计算方法与物理模型本文使用 LAMMPS MD 软件包[26]采用非平衡分子动力学... 　于是我们就石墨烯纳米带扭转成碳纳米管的过 程中, 其热导率的变化进行研究, ...到 MS 软件中进行验证,在进过结构优化后,将模型导入到 Lammps 软件中进行计算... 　石墨烯的杨氏模量, 在理论计算中采用不同的理论计算...多层 石墨烯纳米压痕模拟采用开源软件 Lammps,NVT 系...石墨烯的热导率的分子动... 26页 免费
石墨烯... 　lammps 模拟石墨烯 SiO2 基底接触的热导率 石墨烯 的热导率 如何选择势函...我算过,很坑爹 还是传统的 BKS 势比较适合 hanmd1990 发表于
14... 　lammps振动指令_计算机硬件及网络_IT/计算机_专业资料...(时间单位),单位为 ps 计算公式:T(t) = T0 +...本人意见:这条指令可以用于石墨烯的振动。 4 fix ... 　石墨烯拉伸的in文件_材料科学_工程科技_专业资料。自己写的石墨烯拉伸的in文件,用于lammpstrj 单层石墨烯拉伸 in 文件(lammpstrj) Data 文件:直接可以自己在 VMD ... 　将氧化石墨烯在通 有 NH3 的气氛中进行低温热处理...用 Si 选择性地取代石墨 烯中的 C,并分别计算了...Qin 等[28]利用分子动力学模拟方法 (lammps 程序包...