单原子Lennard-Jones体黏弹性弛豫时间  

Viscoelastic relaxation time of the monoatomic Lennard-Jones system

作　　者：汪杨 赵伶玲 Wang Yang;Zhao Ling-Ling(Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education,School of Energy and Environment,Southeast University,Nanjing 210096,China)

机构地区：[1]东南大学能源与环境学院,能源热转换及其过程测控教育部重点实验室,南京210096

出　　处：《物理学报》2020年第12期12-21,共10页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:51776041)资助的课题.

摘　　要：采用平衡态分子模拟的方法,从微观角度对温度T*=0.85—5、密度ρ*=0.85—1、势参数e=0.97—1和s=0.8—1.3范围内22组液固共存态及液态单原子Lennard-Jones(L-J)体的黏弹性弛豫时间进行了研究,计算了单原子L-J体的静态黏弹性(黏度h*、无限大频率的剪切模量G∞*)及动态黏弹性(储能模量G′*、损耗模量G′′*)等特性参量,并在此基础上分析了黏弹性特征弛豫时间、Maxwell弛豫时间及原子连通弛豫时间.此外,本文根据系统内原子的排布情况,应用Kramers逃逸速率理论描述原子的扩散、汇聚过程,提出并建立了一种单原子L-J体黏弹性弛豫时间的预测方法.结果表明:在单原子L-J体系统中,低温情况下,Maxwell弛豫时间与黏弹性特征弛豫时间差异明显;原子连通弛豫时间与黏弹性特征弛豫时间结果接近,但原子连通弛豫时间的计算过程需耗费大量时间和计算资源;预测方法得到的弛豫时间与黏弹性特征弛豫时间的结果更为接近.本文提出的单原子L-J体黏弹性弛豫时间的预测方法具有一定的准确性和可靠性,可为材料黏弹性弛豫时间的研究提供一种新的思路.Viscoelastic relaxation time is an important concept to characterize the viscoelastic response of materials,which is directly related to the interactions among the microscopic atoms of materials.Few studies have focused on the methods of characterizing viscoelastic relaxation time.To investigate how to represent viscoelastic relaxation time effectively,the viscoelastic relaxation times of the monoatomic Lennard-Jones system on 22 conditions in a range of T*=0.85–5,r*=0.85–1,e=0.97–1,and s=0.8–1.3 are discussed from a microscopic perspective by the equilibrium molecular dynamics methods.Static viscoelasticity(viscosity h*,high-frequency shear modulus G∞*)is calculated by the Green-Kubo formula,and the Fourier transform is applied to the calculation of dynamic viscoelasticity(storage modulus G′*viscoelastic characteristic relaxation time(τMD*),Maxwell relaxation time(τMaxwell*)and the lifetime of the state of local atomic connectivity(τLC*)are calculated.The viscoelastic characteristic relaxation timeτMD*,defined when the two responses crossover,is the key measure of the period of such a stimulus when the storage modulus(elasticity)equals the loss modulus(viscosity).Maxwell relaxation timeτMaxwell*=η*/G∞*,where h*is the static viscosity under infinitely low stimulus frequency(i.e.,zero shear rate),G∞*under infinitely high stimulus frequency,andτLC*neighbor.The result is observed thatτLC*into count the trajectories of all atoms in a certain time range,which takes a lot of time and computing resources.Finally,in order to characterize viscoelastic relaxation time more easily,Kramers’rate theory is used to describe the dissociation and association of atoms,according to the radial distribution functions.And a method of predicting the viscoelasticity of the monoatomic Lennard-Jones system is proposed and established.The comparison of all the viscoelastic relaxation times obtained above shows thatτMaxwell*τMD*But the calculation ofτLC*calculated by our proposed method is closer toτMD*.The met

关 键 词：Lennard-Jones体 分子模拟 黏弹性 弛豫时间 预测方法 

分 类 号：TB303[一般工业技术—材料科学与工程]