Transferability of coarse-grained force fields:: The polymer case
Transferability of coarse-grained force fields:: The polymer case
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DOI：
10.1063/1.2829409
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发表时间：
2008-02-14
影响因子：
4.4
通讯作者：
Mueller-Plathe, Florian
中科院分区：
文献类型：
--
作者：
Carbone, Paola;Varzaneh, Hossein Ali Karimi;Mueller-Plathe, Florian
所有粗粒化方法的一个关键问题是在不同系统和热力学条件之间产生的力场的可转移程度。本文采用迭代玻尔兹曼反演方法，详细研究了粗粒度力场在不同热力学状态下的可转移性。根据原子模拟得到的分布函数对力场进行了优化。我们通过研究聚苯乙烯和聚酰胺-6,6的体积来分析聚合物的情况，它们的粗粒度模型在链长和集中在一个头中的原子数量上有所不同。通过系统地比较粗粒结果和原子结果，测试了温度和压力对材料静态、动态和热力学性能的影响。我们发现描述聚苯乙烯的CG模型只在一个狭窄的温度范围内可转移，当温度比优化模型低80 K时，它不能描述堆积密度的变化。此外，自扩散系数的计算表明，CG模型具有比原子模型更快的动力学特性，并且高估了等温压缩率。相反，聚酰胺-6,6 CG模型在不同热力学条件下是完全可转移的。通过改变模拟的温度或压力来检查可转移性。我们发现，在这种情况下，CG模型能够跟踪所有由温度变化引起的结构内部和结构间重排。此外，在低温下，由于原子系统中存在氢键，原子动力学与原子动力学之间的差异是显著的，而在高温下，原子动力学的加速大大降低，导致原子动力学的扩散系数仅为原子扩散系数的6倍。不同温度下的等温压缩率计算结果与实验结果吻合较好。我们发现聚合物链长度不影响力场的可转移性，我们将这种可转移性主要归因于描述聚酰胺-6,6比聚苯乙烯更精细的模型。(C) 2008年美国物理研究所。
A key question for all coarse-graining methodologies is the degree of transferability of the resulting force field between various systems and thermodynamic conditions. Here we present a detailed study of the transferability over different thermodynamic states of a coarse-grained (CG) force field developed using the iterative Boltzmann inversion method. The force field is optimized against distribution functions obtained from atomistic simulations. We analyze the polymer case by investigating the bulk of polystyrene and polyamide-6,6 whose coarse-grained models differ in the chain length and in the number of atoms lumped in one bead. The effect of temperature and pressure on static, dynamic, and thermodynamic properties is tested by comparing systematically the coarse-grain results with the atomistic ones. We find that the CG model describing the polystyrene is transferable only in a narrow range of temperature and it fails in describing the change of the bulk density when temperature is 80 K lower than the optimization one. Moreover the calculation of the self-diffusion coefficient shows that the CG model is characterized by a faster dynamics than the atomistic one and that it overestimates the isothermal compressibility. On the contrary, the polyamide-6,6 CG model turns out to be fully transferable between different thermodynamic conditions. The transferability is checked by changing either the temperature or the pressure of the simulation. We find that, in this case, the CG model is able to follow all the intra- and interstructural rearrangements caused by the temperature changes. In addition, while at low temperature the difference between the CG and atomistic dynamics is remarkable due to the presence of hydrogen bonds in the atomistic systems, for high temperatures, the speedup of the CG dynamics is strongly reduced, leading to a CG diffusion coefficient only six times bigger than the atomistic one. Moreover, the isothermal compressibility calculated at different temperatures agrees very well with the experimental one. We find that the polymer chain length does not affect the transferability of the force field and we attribute such transferability mainly to the finer model used in describing the polyamide-6,6 than the polystyrene. (C) 2008 American Institute of Physics.