Nonlinear Hydrodynamics of a Hard Sphere Fluid Near the Glas(6)
发布时间:2021-06-08
发布时间:2021-06-08
We conduct a numerical study of the dynamic behavior of a dense hard sphere fluid by deriving and integrating a set of Langevin equations. The statics of the system is described by a free energy functional of the Ramakrishnan-Yussouff form. We find that th
explicitlydemonstratestheexistenceofsuchatransitioninaphysicallyrealisticsystemisnotyetavailable.Thus,the‘thermodynamicglasstransition’scenarioremainsessentiallyspeculative.Inthisapproach,thegrowthoftherelaxationtimeisattributedtoagrowingcorrelationlengthwhichwoulddivergeattheidealglasstransition.Tworecentnumericalstudies25,26whichlookedforsuchagrowingcorrelationlengthdidnot ndanyevidence
27foritsexistence.Arecentexperiment,ontheotherhand,haspresentedevidencefor
theexistenceofalengthscalethatgrowsasthetemperatureisloweredbelowthecrossovertemperatureTc.
Thestaticanddynamicpropertiesofdenseliquidshavealsobeenstudiedexten-sivelybymoleculardynamics(MD)simulations28 32.Theverynatureofthesimulationmethodrestrictssuchstudiestosimplemodelsystemsandtotimescaleswhicharerathershort(oftheorderof10 9sec).Inspiteoftheselimitations,MDsimulationshavepro-ducedanumberofinterestingresultswhichareinqualitativeagreementwithpredictionsofMCtheoriesandresultsofexperiments(suchasthoseusingtheneutronspin-echotech-nique33)whichhavetimescalescomparabletothoseofthesimulations.Thisobservationleadstotheinterestingandusefulconclusionthatastudyofsimplemodelsystemsmaybesu cientforunderstandingthebasicphysicsoftheglasstransition.
Itisevidentfromthisbriefsurveyofthecurrentstatusoftheglasstransitionproblemthatanobviousneedexistsforthedevelopmentofnewanalyticandnumericalmethodswhichmayaddresssomeoftheoutstandingissuesrelatedtothisproblem.Inthispaper,wedescribetheresultsobtainedfromtheapplicationofanewnumericalmethodtoastudyofthedynamicbehaviorofadensehard-sphereliquidneartheglasstransition.ThemethodweuseconsistsofdirectnumericalintegrationofasetofLangevinequationswhichdescribethenonlinear uctuatinghydrodynamics(NFH)
rmation
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