Invariant dynamics in a united-atom model of an ionic liquid

Supporting data and scripts for article, of same title, which is to appear in the Journal of Chemical Physics. Abstract of the article:

We study a united-atom model of the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethyl)sulfonylamide to determine to whatextent there exist curves in the phase diagram along which the microscopic dynamics are invariant when expressed in dimensionless, orreduced, form. The initial identification of these curves, termed isodynes, is made by noting that contours of reduced shear viscosity andreduced self-diffusion coefficient coincide to a good approximation. Choosing specifically the contours of reduced viscosity as nominalisodynes, further simulations were carried out for state points on these, and other aspects of dynamics were investigated to study their degree ofinvariance. These include the mean-squared displacement, shear-stress autocorrelation function, and various rotational correlation functions.These were invariant to a good approximation, with the main exception being rotations of the anion about its long axis. The dynamical featuresthat are invariant have in common that they are aspects that would be relevant for a coarse-grained description of the system. Specifically, removing the most microscopic degrees of freedom in principle leads to a simplification of the potential energy landscape, which allows forthe existence of isodynes.

本数据集为将发表于《Journal of Chemical Physics（化学物理期刊）》的同标题研究论文的配套数据与脚本。论文摘要如下：
本研究以离子液体（ionic liquid）1-丁基-1-甲基吡咯烷双(三氟甲基磺酰)亚胺（1-butyl-1-methylpyrrolidinium bis(trifluoromethyl)sulfonylamide）的联合原子模型（united-atom model）为研究对象，旨在探究相图中存在多少条在以无量纲（或称约化）形式表达时，其微观动力学特性保持不变的曲线。
这类被称为等动力学曲线（isodynes）的曲线，最初通过观察到约化剪切粘度与约化自扩散系数的等值线在良好近似下相互重合而被识别。我们选取约化粘度的等值线作为名义等动力学曲线，针对这些曲线上的状态点开展了进一步模拟，并对动力学的其他方面展开研究以考察其不变性程度。
这些动力学特性涵盖均方位移、剪切应力自相关函数以及各类旋转相关函数。上述特性在良好近似下均保持不变，唯一主要的例外为阴离子绕其长轴的旋转运动。
所有保持不变的动力学特性，其共性在于均与该体系的粗粒化描述相关。具体而言，从理论层面移除最微观的自由度可简化势能面，这为等动力学曲线的存在提供了理论支撑。