Atomistic simulation of the elasticity of polymers
Atomistic simulation of the elasticity of polymers
复制标题
聚合物弹性的原子模拟
DOI：
10.3929/ethz-a-001912968
复制
发表时间：
1997
期刊：
影响因子：
--
通讯作者：
M. Zehnder
中科院分区：
文献类型：
--
作者：
M. Zehnder
在这项工作中，计算了固体，特别是结晶性和非晶性聚合物的弹性常数。第一部分分三章介绍弹性理论、大气模型和涨落理论，为第二部分奠定基础，第二部分给出各种计算机模拟的结果。第一章从应力和应变张量出发，阐述了刚度张量和柔度张量的性质。特别强调对称运算和坐标变换。在原子模型一章中，讨论了分子内和分子间力场的泛函形式和计算，以及相空间的正则采样算法。第三章的重点是从目前整体参数的涨落计算弹性常数的完整张量的方法，有两个这样的公式：第一个公式来自Parnnello和Rahman，只使用晶胞形状的涨落(即相对于参考形状的应变)，第二个公式是在本工作过程中建立的，既考虑了应变的波动，又考虑了应力和应变的相关性。第二部分描述了Ar、聚乙烯、聚丙烯、纤维素、聚酰胺和聚碳酸酯的原子模型的产生。这些模型被MC和MD算法传播到相空间，以比较两种涨落方法的收敛行为，并测试它们对真实聚合物材料的适用性。只有在相空间的遍历采样的极限下，即对于无限长的模拟，才能用涨落方法得出准确的结果。因此，这些算法的收敛行为对于在合理的时间内获得有用的近似是最重要的。可以看出，新的涨落公式至少与公认的Parnnello-Rahman公式收敛得一样好。在某些情况下，新的应力-应变关联法在低温和小振荡情况下甚至要快得多。通过比较这两种方法的结果，可以估计弹性常数的准确性。对于非晶态和晶态聚合物，计算的弹性常数与实验的弹性常数之间都有很好的一致性。与静态最小能量法等其他方法相比，甚至可以预测客体小分子和温度变化对弹性行为的影响。除此之外，还可以使用分子动力学模拟中产生的大量数据来计算动力学性质，如弛豫谱。
In this work, the elastic constants of solids, in particular crystalline and amorphous polymers, are computed numerically. The first part introduces in three chapters to the theory of elasticity, to ato¬ mistic modelling, and to the theory of fluctuations, laying the foundations for the second part, which presents the results of various computer simulations. Starting from the stress and strain tensor, the properties of stiffness and compliance tensors are deployed in the first chapter. Special emphasis is put on symmetry operations and on coordinate transformations. In the chapter about atomistic modelling, the functional form and the computation of intraand intermolecular forcefield terms are covered as well as algorithms for the canonical sampling of the phase space. The focus of the third chapter is on methods that compute the complete tensor of the elastic constants from fluctuations of global parameters At the moment, there are two such formula: The first is from Parnnello and Rahman and uses the fluctuations of the cell shape (i e the strain with respect to a reference shape) only, whereas the second was established in the course of this work and takes into consideration both the fluctuations of the strain and the correlation of stress and strain The generation of atomistic models of argon, polyethylene, polypropylene, cellulose, polyamide, and polycarbonate is described in the second part of this work. These models were propagated by MC and MD algorithms through phase space to compare the convergence behaviour of the two fluctuation approaches and to test their applicability to real polymeric materials. Exact results are deliv¬ ered by fluctuation approaches only in the limit of an ergodic sampling of the phase space, i e for infinitely long simulations. The convergence behaviour of these algorithms is therefore of prime interest to get useful approximations in a reasonable time. It could be shown, that the new fluctuation formula converges at least as good as the well established Parnnello-Rahman formula. In some cases low temperatures and small oscillations the new stress-strain correla¬ tion method is even much faster. Comparison between the results of the two approaches allows for an estimation of the accuracy of the elastic constants There is a good agreement between calculated and experimental elastic constants both for amorphous and crystalline polymers. In contrast to other methods like the static minimum energy method, it was even possible to predict the influence of small guest molecules and of temperature changes on the elas¬ tic behaviour. Besides this, it is possible to use the huge amounts of data pro¬ duced in molecular dynamics simulations to compute dynamic properties like relaxation spectra.
影响因子：
3
作者：
WEINER, SJ;KOLLMAN, PA;CASE, DA
通讯作者：
CASE, DA