Systematic coarse-graining of inhomogeneous systems

宾夕法尼亚州立大学的William Noid教授获得了化学系化学理论、模型和计算方法项目的奖励，以开发界面处软材料的低分辨率（粗粒度（CG））模型。 软材料包括胶体、凝胶、聚合物、液晶、泡沫和生物组织。 界面的一个例子是当液体与空气接触时。界面现象从根本上说是有趣的。 它们还具有巨大的实际意义，因为它们控制着许多现代材料和设备的性能。 由于计算机模拟使我们能够可视化界面的结构，组织，相互作用和变化，它们对帮助我们理解界面现象有很大的希望。 计算机模拟对于设计具有所需材料特性的界面是有用的。 然而，包括界面的所有原子细节的模拟在计算上是非常昂贵的。 这一费用严重限制了它们用于理解界面系统。 粗粒度（CG）模型是较便宜的计算方法。 通过减少分子的细节，CG模型提供了必要的计算效率，有效地模拟长度和时间尺度，不能有效地解决与原子模型。 在这项研究中，Noid教授和他的同事开发了精确描述界面现象的CG模型。 此外，该项目还开发了一个代际科学俱乐部，将宾夕法尼亚州立大学的学生，退休教师和当地退休人员融入以发现为基础的科学教育和话语中。 “自下而上”的CG模型不仅非常有效，而且还提供了均匀材料的结构特性的准确描述。 不幸的是，这些模型通常提供接口和其他非均匀系统的穷人的描述。 因此，本研究的中心目标是开发理论和计算方法，用于参数化和模拟CG模型，准确地模拟非均质系统的结构和热力学性质。 由此产生的洞察力和软件可以实现高效的模拟，提供界面系统的真实描述，并最终指导具有所需界面特性的特定材料系统的设计。为了实现这些目标，该研究开发了严格的理论和数值计算，以了解为什么当前自下而上的模型对非均匀系统的描述很差。 该研究还开发了强大的计算方法来解决实践中的这些限制。 特别是，一个广义的Yvon-Born-Green形式主义量化的力的不平衡，出现在CG接口和照明有用的连接与经典的密度泛函理论的非均匀系统。 巨正则形式主义提供了洞察CG模型的热力学一致性，也确定了有效的潜力，可转移到均匀和非均匀的环境。 由此产生的进步提供了研究软材料界面，特别是固体-液体和聚合物-基材界面的结构和热力学性质的工具。该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估的支持。

Professor William Noid of the Pennsylvania State University is supported by an award from the Chemical Theory, Models and Computational Methods program in the Chemistry division to develop low-resolution (coarse-grained (CG)) models of soft materials at interfaces. Soft materials include colloids, gels, polymers, liquid crystals, foams and biological tissues. An example of an interface is when liquid comes into contact with air. Interfacial phenomena are fundamentally interesting. They also have tremendous practical significance, since they control the performance of many modern materials and devices. Because computer simulation allow us to visualize the structure, organization, interactions and changes of interfaces, they hold great promise for helping us understand interfacial phenomena. Computer simulations are useful for designing interfaces with desired material properties. However, simulations that include all the atomic details of the interface are very computationally expensive. This expense severely limits their use for understanding interfacial systems. Coarse-grained (CG) models are less expensive computational methods. By representing molecules in reduced detail, CG models provide the necessary computational efficiency for effectively simulating length- and time-scales that cannot be effectively addressed with atomistic models. In this research, Professor Noid and his coworkers develop CG models that accurately describe interfacial phenomena. Additionally, this project develops an intergenerational science club that integrates Penn State students, emeritus faculty, and local retirees in discovery-based scientific education and discourse. "Bottom-up" CG models are not only exceedingly efficient, but also provide an accurate description of the structural properties of homogeneous materials. Unfortunately, these models generally provide a poor description of interfaces and other inhomogeneous systems. Accordingly, the central goal of this research is to develop theory and computational methods for parameterizing and simulating CG models that accurately model the structure and thermodynamic properties of inhomogeneous systems. The resulting insight and software may enable highly efficient simulations that provide a realistic description of interfacial systems and, ultimately, guide the design of specific material systems with desired interfacial properties. In order to achieve these goals, the research develops rigorous theory and numerical calculations to understand why current bottom-up models provide a poor description of inhomogeneous systems. The research also develops robust computational methods for addressing these limitations in practice. In particular, a generalized-Yvon-Born-Green formalism quantifies the force imbalances that arise at the CG interfaces and illuminates useful connections with classical density functional theories for inhomogeneous systems. A grand canonical formalism provides insights into the thermodynamic consistency of CG models and also determines effective potentials that are transferable to both homogeneous and inhomogeneous environments. The resulting advances provide tools for investigating soft material interfaces and, in particular, the structure and thermodynamic properties of solid-liquid and polymer-substrate interfaces.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.