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。技术摘要结构-属性关系长期以来一直指导材料发现，并提高了我们对各种物理现象背后机制的理解。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与给定材料性质之间的关系。出发点是集团膨胀形式主义，它可以表达一个标量材料属性和晶体合金之间的关系？的原子构型。本项目将此形式推广到张量值和非均匀/各向异性材料属性。由此产生的广义集团展开与第一性原理计算将应用于三个一般领域：（1）相场建模：广义团簇展开可以编码表示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依赖于环境的力常数张量来确定声子谱中特定特征的原子级起源。在这里，广义集群扩展中的每一项都将提供关于工作机制的独立几何见解。(3)材料发现和/或优化：广义簇展开将被用来展示一个有效的计算组合筛选大量的候选超晶格在搜索一个与器件设计相关的属性的期望组合。在这个项目中开发的软件工具将包括在合金理论自动化工具包，一个广泛使用的软件包，PI已在万维网上提供。该项目将促进研究和教育的整合以及科学的多样性，通过促进加州理工学院建立的材料合作伙伴计划？美国材料科学与工程中心，该中心招收加州洛杉矶州立大学的本科生，与加州理工学院合作开展研究项目。非技术性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，用于确定特定材料（可能是候选材料）的结构与其性能之间的关系。PI将扩展现有方法，以包含更大的材料属性集，从而增强该方法的能力和实用性。研究工作有助于通过计算发现具有所需特性的新材料，并且仅从组成原子的身份开始。这项研究可能导致发现具有技术应用所需特性的新材料，或优化现有材料或材料结构的特性。用于光电器件的新材料是该项目的一个具体重点。 在这个项目中开发的软件工具将提供给更广泛的材料研究界，并将有助于其网络基础设施。

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.