MOLECULAR-DYNAMICS SIMULATION OF A POLYMER-CHAIN IN SOLUTION
MOLECULAR-DYNAMICS SIMULATION OF A POLYMER-CHAIN IN SOLUTION
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DOI：
10.1063/1.465445
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发表时间：
1993-11-01
影响因子：
4.4
通讯作者：
KREMER, K
中科院分区：
文献类型：
--
作者：
DUNWEG, B;KREMER, K
一个单一的聚合物链在良好的溶剂中的分子动力学模拟的结果。后者被明确地建模为粒子浴。该系统提供了一个第一性原理的微观测试链的布朗运动的流体动力学Kirkwood-Zimm理论。在4066溶剂颗粒以及40/4056和60/7940体系中研究了30单体链。密度选择得相当高，以便接近不可压缩流的理想情况，并确保扩散动量传输比粒子运动快得多。为了科普微正则算法的数值不稳定性，我们生成的初始状态的朗之万模拟，其中包括耦合到一个热浴，这是关闭的动力学分析。长范围的流体动力学相互作用诱导的扩散性能，这是可观察到的链和溶剂颗粒的扩散常数的有限盒大小的大的影响。将扩散常数的柯克伍德理论和动态光散射中初始衰减率的Akcasu等人的理论推广到有限盒的情形，用相应的Ewald和代替Oseen张量。在前导顺序中，有限大小校正与线性盒尺寸成反比。考虑到这一理论修正，验证了扩散常数的柯克伍德公式。此外，单体运动表现出的缩放，这是更接近Zimm比劳斯指数（t2/3法律的均方位移的动态结构因子的衰减率是成比例的k3）。然而，前因子与理论并不一致，表明（在所涉及的短尺度上）动力学比简单的流体动力学描述更复杂。
Results of a molecular dynamics simulation of a single polymer chain in a good solvent are presented. The latter is modeled explicitly as a bath of particles. This system provides a first-principles microscopic test of the hydrodynamic Kirkwood-Zimm theory of the chain's Brownian motion. A 30 monomer chain is studied in 4066 sol vent particles as well as 40/4056 and 60/7940 systems. The density was chosen rather high, in order to come close to the ideal situation of incompressible flow, and to ensure that diffusive momentum transport is much faster than particle motions. In order to cope with the numerical instability of microcanonical algorithms, we generate starting states by a Langevin simulation that includes a coupling to a heat bath, which is switched off for the analysis of the dynamics. The long range of the hydrodynamic interaction induces a large effect of finite box size on the diffusive properties, which is observable for the diffusion constants of both the chain and the solvent particles. The Kirkwood theory of the diffusion constant, as well as the Akcasu et al. theory of the initial decay rate in dynamic light scattering are generalized for the finite box case, replacing the Oseen tensor by the corresponding Ewald sum. In leading order, the finite-size corrections are inversely proportional to the linear box dimensions. With this modification of the theory taken into account, the Kirkwood formula for the diffusion constant is verified. Moreover, the monomer motions exhibit a scaling that is much closer to Zimm than to Rouse exponents (t2/3 law in the mean square displacement; decay rate of the dynamic structure factor is-proportional-to k3). However, the prefactors are not consistent with the theory, indicating that (on the involved short length scales) the dynamics is more complex than the simple hydrodynamic description suggests.