CAREER: Toward Rational Discovery and Design of Metastable Materials

物质的亚稳态形式在它们倾向于转变为热力学上更有利的稳定形式的环境和条件下长期存在。在我们的日常生活中，这样的材料有很多例子。最著名的例子是钻石，这是一种晶体形式的碳，在室温和环境压力下是亚稳态的。在这些条件下，金刚石会自发地转变为石墨，但这个过程非常缓慢，使得金刚石的寿命足够长（亚稳态），因此它的机械、光学和电子特性可以在许多技术相关的应用中得到利用。其他著名的例子还有玻璃，它是二氧化硅的一种非晶体亚稳态形式，以及固态巧克力的所谓多晶型v型，由于其理想的熔化性、质地和口感特征，这是它最常用的形式。尽管亚稳态材料的重要性已经得到证实，尽管我们对亚稳态现象学有相当广泛的了解，但我们为特定目的预测和设计亚稳态物质形式的能力相当有限。巨大的知识缺口仍然存在，这阻碍了准确预测在众多可能性中，哪些亚稳态实际上可以通过实验实现，以及它们倾向于在这种状态下保持多长时间。该项目的主要科学目标是填补这些知识空白，以便合理可靠地发现和设计亚稳材料。更具体地说，这个项目集中在理论发展，以提高我们的理解和我们的能力，以预测模型亚稳态的可实现性和它们的转化动力学热力学更稳定的形式。这将通过结合现代电子结构方法和分子动力学模拟，以及利用PI以前的成就和他的团队现有的能力来实现。这个项目旨在整合新产生的知识的教育和推广活动包括：(i)开发旨在促进学生参与和主动学习的创新课程材料；（ii）通过本项目创造的机会增加本科生对研究的参与，并继续参与国家可再生能源实验室能源科学系本科生实验室实习计划；（iii）加强PI在科罗拉多矿业学院转校生成功的桥梁机会项目中的作用，该项目旨在通过暑期研究经验从社区学院招收和留住转校生。教育和推广活动还将包括在主要材料科学和凝聚态物理会议上组织教程和专题讨论会，以及通过出版物和演讲进行传播。亚稳态系统，包括晶体（多晶）和非晶体（玻璃状，无定形），为发现新颖有用的材料提供了广阔而丰富的空间，但实际上尚未开发。虽然在我们的日常生活中有许多亚稳态材料的例子（例如钻石，玻璃，巧克力，锐钛矿），但我们目前对亚稳态的理解主要是现象学和定性的。首先，我们才刚刚开始了解亚稳态多晶的可实现性；也就是说，与大量可能的低能态相比，为什么只有少量的结构在实验中实现。第二，不像基态是稳定的，亚稳态有有限的寿命，我们预测不同相之间转化动力学的能力目前相当有限。这些评论也适用于我们对结构-性质关系的理解；与结构改变会产生什么影响相比，我们更了解改变化学会如何影响材料的相关特性。这个项目的主要目标是填补这些知识空白；具体目标包括：(1)扩展我们对控制亚稳晶相可实现性的物理原理的理解，(2)实现玻璃态和非晶态的预测建模，以及(3)揭示控制不同晶体结构之间转化动力学的物理原理。这将通过结合现代电子结构方法和分子动力学模拟，以及利用PI以前的成就和他的团队现有的能力来实现。这项工作是建立在假设亚稳固体的可实现性，特别是晶体多晶，是由它们的热力学概率决定的，并且多晶转变的快速或缓慢的动力学性质主要是晶体学的主要贡献。这些假设在PI的初步工作中得到了部分验证，为我们目前对亚稳态的认识奠定了基础，并为创造强大而有效的计算方法奠定了基础，这些方法将使我们能够识别新的和潜在的突破性亚稳态功能材料。这个项目旨在整合新产生的知识的教育和推广活动包括：(i)开发旨在促进学生参与和主动学习的创新课程材料；（ii）通过本项目创造的机会增加本科生对研究的参与，并继续参与国家可再生能源实验室能源科学系本科生实验室实习计划；（iii）加强PI在科罗拉多矿业学院转校生成功的桥梁机会项目中的作用，该项目旨在通过暑期研究经验从社区学院招收和留住转校生。教育和推广活动还将包括在主要材料科学和凝聚态物理会议上组织教程和专题讨论会，以及通过出版物和演讲进行传播。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

NONTECHNICAL SUMMARYMetastable forms of matter are long-lived in environments and conditions at which they would tend to transform to more thermodynamically favorable stable forms. There are many examples of such materials in our daily lives. The best-known example is diamond, a crystalline form of carbon that is known to be metastable at room temperature and ambient pressure. At these conditions diamond would tend to spontaneously transform into graphite, but this process is extremely slow making diamond sufficiently long-lived (metastable) so that its mechanical, optical and electronic properties can be utilized in a number of technologically relevant applications. Other well-known examples are glass, which is a non-crystalline metastable form of silicon dioxide, and solid chocolate in the so-called polymorph-V form, which is its most utilized form due to its desired melting, textural and mouth-feel characteristics. Despite the proven importance of metastable materials and despite a rather extensive knowledge of the phenomenology of metastability, our ability to predict and design metastable forms of matter for a specific purpose is rather limited. Significant knowledge gaps remain that prevent accurate predictions of which metastable states, out of the numerous possibilities, could actually be experimentally realized and how long they would tend to remain in that state.The main scientific goal of this project is to fill these knowledge gaps in order to enable rational and reliable discovery and design of metastable materials. More specifically, this project concentrates on theory developments to advance our understanding and our ability to predictively model the realizability of metastable states and the kinetics of their transformations to thermodynamically more stable forms. This will be achieved through a combination of modern electronic structure methods and molecular dynamics simulations, as well as by leveraging previous accomplishments of the PI and the existing capabilities present in his group.The educational and outreach activities of this project aimed to integrate the newly generated knowledge include: (i) development of innovative course materials designed to promote student engagement and active learning, (ii) increasing participation of undergraduates in research both through opportunities created by this project, and continuing participation in the Department of Energy Science Undergraduate Laboratory Internships program at the National Renewable Energy Laboratory, and (iii) strengthening PI’s role in the Bridge Opportunities for Transfer Student Success program at the Colorado School of Mines that seeks to both recruit and retain transfer students from community colleges through summer research experiences. Educational and outreach activities will also include organization of tutorials and symposia at major materials science and condensed matter physics conferences as well as dissemination through publications and presentations.TECHNICAL SUMMARYMetastable systems, both crystalline (polymorphs) and non-crystalline (glassy, amorphous), offer a vast and immensely rich, but virtually unexplored space for discovering novel and useful materials. While there are many examples of metastable materials in our daily lives (e.g. diamond, glass, chocolate, anatase), our present understanding of metastability is largely phenomenological and qualitative. First, we are only beginning to understand the realizability of metastable polymorphs; that is, why there is only a small number of structures realized experimentally in comparison to the large number of possible low-energy states. Second, unlike the ground states which are stable, the metastable states have finite lifetimes and our ability to predict kinetics of transformations between different phases is presently rather limited. These remarks also apply to our understanding of the structure-property relations; we understand much better how changing the chemistry would affect relevant properties of materials compared to what would happen if the structure changed.The main goal of this project is to fill these knowledge gaps; with the specific objectives which include: (i) extending our understanding of physical principles governing realizability of metastable crystalline phases, (ii) enabling predictive modeling of glassy and amorphous states, and (iii) revealing physical principles governing kinetics of transformations between different crystal structures. This will be achieved through a combination of modern electronic structure methods and molecular dynamics simulations, as well as by leveraging previous accomplishments of the PI and the existing capabilities present in his group. The work is founded on the hypotheses that the realizability of metastable solids, in particular crystalline polymorphs, is determined by their thermodynamic probabilities and that the dominant contributions to the rapid or slow nature of the kinetics of polymorphic transformations are primarily crystallographic. These hypotheses, which are partially validated in the PI’s preliminary work, form a basis to both advance our present state of knowledge of metastability and for creating powerful and efficient computational methodologies that would enable identification of new and potentially ground-breaking metastable functional materials. The educational and outreach activities of this project aimed to integrate the newly generated knowledge include: (i) development of innovative course materials designed to promote student engagement and active learning, (ii) increasing participation of undergraduates in research both through opportunities created by this project, and continuing participation in the Department of Energy Science Undergraduate Laboratory Internships program at the National Renewable Energy Laboratory, and (iii) strengthening PI’s role in the Bridge Opportunities for Transfer Student Success program at the Colorado School of Mines that seeks to both recruit and retain transfer students from community colleges through summer research experiences. Educational and outreach activities will also include organization of tutorials and symposia at major materials science and condensed matter physics conferences as well as dissemination through publications and presentations.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.