Direct construction of mesoscopic models from microscopic simulations.
Direct construction of mesoscopic models from microscopic simulations.
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DOI：
10.1103/physreve.81.026704
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发表时间：
2010-02
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影响因子：
--
通讯作者：
Karniadakis GE
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文献类型：
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作者：
Lei H;Caswell B;Karniadakis GE
从约束Lennard-Jones（LJ）团簇（具有恒定回转半径Rg）的微观分子动力学（MD）模拟出发，通过将LJ团簇粗粒化为单个粒子，构建了两个介观模型[Langevin动力学和耗散粒子动力学（DPD）]。粗粒度模型的静态和动态性能进行了研究，并与MD结果进行了比较。有效的平均力场被计算为簇间距离的函数，并且相应的势与每个簇的粒子数和温度成线性比例。我们验证了平均力场可以在很宽的密度范围内再现原子系统的状态方程，但径向分布函数只能在稀态和半稀态。两种模型的摩擦力系数直接从微观系统的随机力场的时间相关函数计算。对于高密度或一个大的集群大小的摩擦力被高估和低估的扩散率由于遗漏的多体效应作为一个结果的假设成对形式的粗粒力场。当多体效应不那么明显时（例如，对于较小的Rg或半稀释体系），DPD模型可以再现MD体系的动力学特性。
Starting from microscopic molecular-dynamics (MD) simulations of constrained Lennard-Jones (LJ) clusters (with constant radius of gyration Rg), we construct two mesoscopic models [Langevin dynamics and dissipative particle dynamics (DPD)] by coarse graining the LJ clusters into single particles. Both static and dynamic properties of the coarse-grained models are investigated and compared with the MD results. The effective mean force field is computed as a function of the intercluster distance, and the corresponding potential scales linearly with the number of particles per cluster and the temperature. We verify that the mean force field can reproduce the equation of state of the atomistic systems within a wide density range but the radial distribution function only within the dilute and the semidilute regime. The friction force coefficients for both models are computed directly from the time-correlation function of the random force field of the microscopic system. For high density or a large cluster size the friction force is overestimated and the diffusivity underestimated due to the omission of many-body effects as a result of the assumed pairwise form of the coarse-grained force field. When the many-body effect is not as pronounced (e.g., smaller Rg or semidilute system), the DPD model can reproduce the dynamic properties of the MD system.