Roberto - Improved dynamics in self-consistent-field molecular-dynamics simulations of polymers

Roberto - 改进聚合物自洽场分子动力学模拟的动力学

• 批准号: 333583913
• 负责人: Professor Dr. Florian Müller-Plathe
• 金额: --
• 依托单位: Fachgebiet Physikalische Chemie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2017-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/333583913?language=en
• 关键词: Roberto; Improved; dynamics; self; consistent

The main objective is to develop a new molecular-simulation algorithm, which allows the investigation of phenomena in polymer and especially nanocomposites that are scientifically interesting and technologically relevant, but which hitherto cannot be simulated. This is commonly the case, because available compute power is not sufficient to simultaneously use realistic models, model large enough samples, and simulate them long enough to observe all relevant physical processes.Our proposed approach combines two recently developed methods. The first ingredient is the so-called self-consistent-field MD method (MD-SCF) of Milano (Salerno) and Kawakatsu (Sendai). It accelerates the calculation of the compute-intensive nonbonded interactions by an auxiliary field representation. It can be used with both atomistic and coarse-grained polymer models and has been shown to reproduce molecular structure and thermodynamic properties of polymer materials very accurately at low computational cost. By design, however, it is unable to capture correctly the molecular dynamics of polymers and all properties resulting from it, such as diffusion, melt viscosity and rheological parameters. This failure results from the lack of excluded-volume interactions between beads of different chains in the MD-SCF model. Chain crossing is not prevented, chain entanglement and reptation are absent, and a qualitatively wrong polymer dynamics results.At this point, the second ingredient enters. Working with Masubuchi (Nagoya), we have recently developed the concept of temporary mobile cross-links between polymer chains as a mock-up for entanglements. We have implemented these so-called slip-links successfully into the dissipative-particle-dynamics (DPD) model for polymers. DPD also lacks a hard-core repulsion between beads and has exactly the same problems with the polymer dynamics as has MD-SCF. After the intro-duction of slip-links, however, DPD reproduced all essential features of polymer melt dynamics. We will therefore implement slip-links into the MD-SCF method as well, which is an improvement over DPD, because it allows for more chemical specificity.The project phases are: (1) Development and implementation of the MD-SCF/slip-link combination and its technical validation. (2) Addressing a number of scientific risks, which might cause the method to fail in certain cases. For example, introducing slip-springs into the Hamiltonian could shift the calculated properties to such an extent that they would have to be compensated in some way. (3) Finding a range of the operational parameters of the new method which is suitable for the calculation of dynamical properties of polymers. (4) Finally, we would like to do a first application of the new method to very recent problems involving rheological and other dynamical properties of polymer composites, which can be addressed by other methods only with difficulties or not at all.

主要目的是开发一种新的分子模拟算法，该算法允许研究聚合物现象，尤其是纳米复合材料，这些现象在科学上有趣且技术上相关，但迄今无法模拟。通常情况下是这种情况，因为可用的计算功率不足以同时使用现实的模型，模拟足够大的样本并将其模拟足够长的时间以观察所有相关的物理过程。我们所提出的方法结合了两种最近开发的方法。第一种成分是Milano（Salerno）和Kawakatsu（sendai）的所谓自洽场MD方法（MD-SCF）。它通过辅助场表示加速了计算密集型非键相互作用。它可以与原子和粗粒聚合物模型一起使用，并已被证明可以以低计算成本非常准确地重现聚合物材料的分子结构和热力学特性。然而，通过设计，它无法正确捕获聚合物的分子动力学以及由其产生的所有特性，例如扩散，融化粘度和流变参数。由于MD-SCF模型中不同链的珠子之间缺乏排除的体积相互作用而导致这种故障。没有阻止链条交叉，链条纠缠和仓库不存在，质量错误的聚合物动力学结果。在这一点上，第二个成分进入。与Masubuchi（Nagoya）合作，我们最近开发了聚合物链之间的临时移动交联概念，作为纠缠的模型。我们已经成功地将这些所谓的滑移链链接到了用于聚合物的耗散粒子 - 动力学（DPD）模型中。 DPD还缺乏珠子之间的硬核排斥，并且与MD-SCF的聚合物动力学完全相同。然而，在滑动链接的介绍后，DPD再现了聚合物熔体动力学的所有基本特征。因此，我们还将在MD-SCF方法中实现滑移链接，这是对DPD的改进，因为它允许更具化学特异性。项目阶段是：（1）MD-SCF/Slip-Link组合的开发和实施及其技术验证。 （2）解决许多科学风险，这可能导致该方法在某些情况下失败。例如，将滑弹性引入哈密顿量可以将计算出的属性转移到一定程度上，以至于必须以某种方式得到补偿。 （3）找到适合计算聚合物动力学特性的新方法的一系列操作参数。 （4）最后，我们想将新方法的首次应用于涉及聚合物复合材料的流变学和其他动力学特性的最新问题，这些方法只能通过其他方法来解决，或根本没有困难。