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arXiv 1306.5555cond-mat.soft
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用多重围道积分构成的简单结不变量研究polymer结

A study of polymer knots using a simple knot invariant written consisting of multiple contour integrals

Yani Zhao, Franco Ferrari

摘要:

在这项工作中,短的聚合物节(多达120段)定义在一个简单的立方晶格的热力学性质的帮助下,Wang-Landau Monte Carlo算法进行了研究。使用从给定种子构造开始的枢轴变换来执行采样过程。短程吸引力和排斥力作用于单体的情况下被认为是。讨论了几种节子的比能、热容和回转半径的性质。结果表明,热容呈现出一个尖锐的峰值。如果相互作用是有吸引力的,在单个开链中也观察到类似的峰,并且与从冷冻微晶状态到膨胀卷曲状态的转变有关。分析的可观的行为的一些其他特点,例如增加或减少的结比能量在高温下随着聚合物长度的增加,取决于如果相互作用是吸引或排斥。除了研究聚合物结的热力学外,本文的第二个目标是介绍一种基于拓扑不变量来区分结的拓扑的方法,该拓扑不变量是多重围道积分的形式,并且显式地依赖于结的物理轨迹。所选择的不变量与Conway多项式的第二个系数有关。它首次从具有规范群SU(N)的陈-西蒙斯场论的振幅中分离出来。结果表明,该不变量在区分高分子结的拓扑结构方面是非常可靠的。所提出的方法的优点之一是,它允许减少所需的Wang-Landau算法的样本的数量。一些解决方案,以加快计算利用蒙特卡罗积分技术的发展。

英文摘要:

In this work the thermodynamic properties of short polymer knots (up to 120 segments) defined on a simple cubic lattice are studied with the help of the Wang-Landau Monte Carlo algorithm. The sampling process is performed using pivot transformations starting from a given seed conformation. Both cases of short-range attractive and repulsive interactions acting on the monomers are considered. The properties of the specific energy, heat capacity and gyration radius of several knots are discussed. It is found that the heat capacity exhibits a sharp peak. If the interactions are attractive, similar peaks have been observed also in single open chains and have been related to the transition from a frozen crystallite state to an expanded coil state. Some other peculiarities of the behavior of the analyzed observables are presented, like for instance the increasing or decreasing of the knot specific energy at high temperatures with increasing polymer lengths depending if the interactions are attractive or repulsive. Besides the investigation of the thermodynamics of polymer knots, the second goal of this paper is to introduce a method for distinguishing the topology of a knot based on a topological invariant which is in the form of multiple contour integrals and explicitly depends on the physical trajectory of the knot. The chosen invariant is related to the second coefficient of the Conway polynomial. It has been first isolated from the amplitudes of a Chern-Simons field theory with gauge group SU(N). It is shown that this invariant is very reliable in distinguishing the topology of polymer knots. One of the advantages of the proposed approach is that it allows to reduce the number of samples needed by the Wang-Landau algorithm. Some solutions to speed up the calculations exploiting Monte Carlo integration techniques are developed.

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