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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >Derivation of Coarse Grained Models for Multiscale Simulation of Liquid Crystalline Phase Transitions
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Derivation of Coarse Grained Models for Multiscale Simulation of Liquid Crystalline Phase Transitions

机译：液晶相变多尺度模拟的粗粒度模型的推导

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We present a systematic derivation of a coarse grained (CG) model for molecular dynamics (MD) simulations of a liquid crystalline (LC) compound containing an azobenzene mesogen. The model aims at a later use in a multiscale modeling approach to study liquid crystalline phase transitions that are (photo) induced by the trahs/cis photoisomerization of the mesogen. One of the major challenges in the coarse graining process is the development of models that are for a given chemical system structurally consistent with for example an all-atom reference model and reproduce relevant thermodynamic properties such as the LC phase behavior around the state point of interest. The reduction of number of degrees of freedom makes the resulting coarse models by construction state point dependent; that is, they cannot easily be transferred to a range of temperatures, densities, system compositions, etc. These are significant challenges, in particular if one wants to study LC phase transitions (thermally or photoinduced). In the present paper we show how one can systematically derive a CG model for a LC molecule that is highly consistent with an atomistic description by choosing an appropriate state point for the reference simulation. The reference state point is the supercooled liquid just below the smectic-isotropic phase transition which is characterized by a high degree of local nematic order while being overall isotropic. With the resulting CG model it is possible to switch between the atomistic and the CG levels (and vice versa) in a seamless manner maintaining values of all the relevant order parameters which describe the smectic A (smA) state. This model will allow us in the future to link large length scale and long time scale CG simulations of the LC state with chemically accurate QM/MM simulations of the photoisomerization process.
机译：我们提出了一个粗粒（CG）模型的系统推导，该模型用于包含偶氮苯液晶元的液晶（LC）化合物的分子动力学（MD）模拟。该模型旨在以后在多尺度建模方法中使用，以研究液晶基相转变，该液晶相变是由液晶元的trahs / cis光异构化诱导的（光）。粗粒化过程中的主要挑战之一是针对给定化学系统的模型开发，该模型在结构上与例如全原子参考模型保持一致，并重现相关的热力学性质，例如感兴趣状态点周围的LC相行为。 。自由度数量的减少使生成的粗略模型受构造状态点的影响;也就是说，它们不容易转移到一定范围的温度，密度，系统组成等范围。这是很大的挑战，特别是如果要研究LC相变（热或光诱导）时。在本文中，我们展示了如何通过为参考模拟选择合适的状态点来系统地推导与原子描述高度一致的LC分子的CG模型。参考状态点是在近晶各向同性相变之下的过冷液体，其特征在于高度局部向列相，而整体上各向同性。使用所得的CG模型，可以以无缝方式在原子级和CG级之间切换（反之亦然），并保持描述近晶A（smA）状态的所有相关有序参数的值。该模型将使我们将来能够将LC状态的大长度尺度和长时间尺度CG模拟与光异构化过程的化学精确的QM / MM模拟联系起来。

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