The spherical representation usually utilized for the coarse-grained particles of soft matter systems is an assumption and pertinent studies have shown that both structural and dynamical properties can depend on anisotropic effects. On these grounds, we develop coarse-grained equations of motion which take into account explicitly the anisotropy of the beads. As a first step, this model incorporates only conservative terms. Inclusion of the dissipative and random terms is in principle possible but is beyond the scope of this study. The translational dynamics of the beads is tracked using the position and momentum of their center of mass, while their rotational dynamics is modeled by representing their orientation through the use of quaternions, similarly to the case of rigid bodies. The associated force and torque controlling the motion are derived from atomistic molecular dynamics (MD) simulations via a bottom-up approach and define a coarse-grained potential. The assumptions of the model are clearly stated and checked for a reference system of a cis-1,4-polybutadiene melt. In particular, the choice of the angular velocity as a slow variable is justified by comparing its dynamics to atomic vibrations. The accuracy of this approach to reproduce static structural features of the polymer melt is assessed.

中文翻译：

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评估顺式-1,4-聚丁二烯的各向异性粗粒模型：自下而上的方法

通常用于软物质系统的粗粒颗粒的球形表示是一个假设，相关研究表明，结构和动力学特性都可能取决于各向异性效应。基于这些理由，我们开发了粗粒度的运动方程，该方程明确考虑了磁珠的各向异性。第一步，此模型仅包含保守术语。原则上可以包括耗散和随机项，但这不在本研究的范围之内。珠的平移动力学是使用其质心的位置和动量来跟踪的，而其旋转动力学是通过使用四元数表示其取向来建模的，这与刚体的情况类似。通过自下而上的方法并定义粗粒度的潜力。明确陈述了模型的假设，并检查了顺式-1,4-聚丁二烯熔体的参考体系。特别地，通过将​​角速度的动力学与原子振动进行比较来证明选择角速度作为慢变量是合理的。评估了该方法重现聚合物熔体静态结构特征的准确性。