The Generalized Cluster Expansion: A Tool for Representing Structure-Property Relationships

该奖项是根据2009年美国复苏和再投资法案(公法111-5)资助的。技术和财产关系长期以来一直指导着材料的发现，并提高了我们对各种物理现象背后的机制的理解。该奖项支持开发一套理论和计算工具，以确定并有效地表示化合物的原子结构和给定材料性质之间的关系。本文的出发点是团簇展开理论，它可以表达标量材料性质与晶态合金--S原子组态之间的关系。这个项目将这种形式推广到张量值和非均匀/非各向同性的材料性质。由此产生的广义团簇展开与第一性原理计算将应用于三个一般领域：(1)相场模拟：广义团簇展开可以编码代表合金有序状态的各种相场与张量性质之间的关系，例如进入模拟系统的介观运动方程的弹性常数或晶格参数。(2)原子机制的自动发现：一个说明性的应用是通过使用环境相关的力常数来确定声子谱中特定特征的原子能级起源。在这里，广义团簇展开中的每一项都将提供关于工作机制的独立的几何洞察。(3)材料发现和/或优化：广义团簇展开将用于演示对大量候选超晶格进行有效的计算组合筛选，以寻找具有与器件设计相关的所需属性组合的超晶格。本项目中开发的软件工具将包括在合金理论自动化工具包中，这是PI在万维网上提供的一个广泛使用的软件包。该项目将通过为加州理工大学S材料科学与工程中心建立的材料伙伴计划做出贡献，促进研究和教育的整合以及科学的多样性。该计划在与加州理工大学的合作研究项目中从加州州立大学洛杉矶分校招募本科生。非技术总结该奖项支持理论和计算研究，这些研究将开发新的计算算法和工具，用于确定特定的、可能的候选材料的结构和性能之间的关系。PI将扩展现有的方法，以允许包含更大的材料属性集，以增强该方法的能力和实用性。这项研究工作有助于通过计算发现具有所需性质的新材料，并仅从组成原子的身份开始。这项研究可能导致发现具有所需性能的新材料用于技术应用，或者优化现有材料或材料结构的性能。光电子器件的新材料是这个项目的一个特别关注的焦点。在该项目中开发的软件工具将向更广泛的材料研究界提供，并将为其网络基础设施作出贡献。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).TECHNICAL SUMMARYStructure-property relationships have long guided materials discovery and improved our understanding of the mechanisms underlying diverse physical phenomena. This award supports developing a set of theoretical and computational tools to determine and efficiently represent the relationship between the atomic structure of a compound and a given material property. The starting point is the cluster expansion formalism, which can express the relationship between a scalar material property and a crystalline alloy?s atomic configuration. This project generalizes this formalism to tensor-valued and nonuniform/nonisotropic material properties.The resulting generalized cluster expansion coupled with first-principles calculations will be applied in three general areas:(1) Phase field modeling: the generalized cluster expansion can encode the relationship between various phase fields representing the state of order of an alloy and tensorial properties, such as elastic constants or lattice parameters that enter the mesoscopic equation of motion of the simulated system.(2) Automated discovery of atomistic mechanisms: An illustrative application is the determination of the atomic-level origins of specific features in the phonon spectrum through the use of environment-dependent force constants tensors. Here, each term in the generalized cluster expansion would provide independent geometrical insight regarding the mechanisms at work.(3) Materials discovery and/or optimization: The generalized cluster expansion will be used to demonstrate an efficient computational combinatorial screening of a large number of candidate superlattices in search of one with the desired combination of properties relevant for device design.Software tools developed in this project will be included within the Alloy Theoretic Automated Toolkit, a widely used software package that the PI has made available on the world-wide web. This project will promote integration of research and education as well as diversity in science by contributing to the Materials Partnership Program established by Caltech?s Center for the Science and Engineering of Materials which recruits undergraduates from California State University, Los Angeles in collaborative research projects with Caltech.NON-TECHNICAL SUMMARYThis award supports theoretical and computational research that will develop new computational algorithms and tools for determining the relationship between the structure of a specific, possibly candidate, material and its properties. The PI will extend an existing approach to enable inclusion of a larger set of materials properties that enhance the power and utility of the method. The research effort contributes to the effort to discover new materials with desired properties using computation and starting only with the identity of the constituent atoms. This research may lead to the discovery of new materials with desired properties for technological applications, or optimizing the properties of existing materials or materials structures. New materials for optoelectronic devices are a specific focus of this project. Software tools developed in this project will be made available to the broader materials research community and will contribute to its cyberinfrastructure.