Lussetti Enrico, Terao Takamichi, Müller-Plathe Florian
Eduard-Zintl-Institut für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Petersenstrasse 20, D-64287 Darmstadt, Germany.
J Phys Chem B. 2007 Oct 4;111(39):11516-23. doi: 10.1021/jp0737956. Epub 2007 Sep 7.
The thermal conductivity of the amorphous phase of polyamide-6,6 is investigated by nonequilibrium molecular dynamics simulations. Two different algorithms are used, reverse nonequilibrium molecular dynamics and the dual-thermostat method. Particular attention is paid to the force field used. Four different models are tested, flexible and rigid bonds and all-atom and united-atom descriptions. They mainly differ in the number of high-frequency degrees of freedom retained. The calculated thermal conductivity depends systematically on the number of degrees of freedom of the model. This dependence is traced to the quantum nature of the fast molecular vibrations, which are incorrectly described by classical mechanics. The best agreement with experiment is achieved for a united-atom model with all bonds kept rigid. It could be shown that both the thermal conductivity and the heat capacity of a model show a similar (but not equal) dependence on its number of degrees of freedom. Hence, the computationally more convenient heat capacity can be used for force field optimization. A side result is the anisotropy of the thermal conductivity in stretched polyamide; heat conduction is faster parallel to the drawing direction than perpendicular to it.
通过非平衡分子动力学模拟研究了聚酰胺-6,6非晶相的热导率。使用了两种不同的算法，即反向非平衡分子动力学和双恒温器方法。特别关注所使用的力场。测试了四种不同的模型，包括柔性键和刚性键以及全原子和联合原子描述。它们的主要区别在于保留的高频自由度数量。计算得到的热导率系统地取决于模型的自由度数量。这种依赖性可追溯到快速分子振动的量子性质，而经典力学对其描述有误。对于所有键均保持刚性的联合原子模型，与实验结果的吻合度最佳。可以表明，模型的热导率和热容对其自由度数量呈现出相似（但不相等）的依赖性。因此，计算上更便捷的热容可用于力场优化。一个附带的结果是拉伸聚酰胺中热导率的各向异性；平行于拉伸方向的热传导比垂直于拉伸方向的热传导更快。
