Collaborative Research: Ab Initio Computation of Phonon Thermal Transport in Crystalline and Disordered Materials

1066406斯图尔特晶格热导率是一个基本的热传输参数，决定了材料在特定热管理应用中的效用。晶格热导率的精确理论建模对于包括微电子冷却、热电甚至行星科学在内的许多领域都是必不可少的。 波士顿学院和康奈尔大学之间的这项合作研究工作的目标将是实施一种理论方法，从第一原理计算晶体和合金材料的晶格热导率。该方法的一个主要特点是没有可调参数，康奈尔大学的研究中心将致力于计算被研究材料和结构的原子间力常数（IFC）。 这些计算将基于密度泛函微扰理论。 IFC是声子色散、声子态密度和声子热输运计算所需的输入，从中获得晶格热导率。 在这个项目中要研究的材料包括铅硫族化物，I-V-VI 2半导体，和纳米颗粒合金结构。第一性原理方法已经证明了与测量的IV族半导体的高热导率非常一致。在这个项目中要研究的材料是统一的，其异常低的热导率，因此提供了一个很好的测试理论的鲁棒性。 许多这些材料的测量的热性能的特点，并将提供一个重要的检查，我们计算的可调参数的自由结果。与测量数据的良好一致性将进一步验证这一最先进理论在研究和理解许多热管理应用中各种材料的热输运和晶格热导率方面的预测能力。目前材料晶格热导率的理论通常是基于高度参数化的弛豫时间近似或基于纯经典的分子动力学模型。动力学计算这里提出的严格的第一性原理理论没有可调的参数，并充分纳入了量子力学声子散射过程。因此，它可以提供目前不可用的预测能力，以支持正在进行的和未来的实验研究的材料中的热传输，以及有助于开发新的高效材料设计所需的热管理application.Broader影响：该项目将提供一个博士后研究员在康奈尔大学和一个博士研究生在波士顿学院的培训。 此外，一些本科生，包括那些来自代表性不足的群体将通过NSF REU计划在波士顿学院和康奈尔大学的网站参加。 该项目期间开发的计算工具将被纳入康奈尔纳米科学技术设施（CNF）的公共计算库。 该活动还将通过帮助开发具有所需热传输特性的新材料来造福社会。这将促进技术突破，可能导致下一代热电材料，热障涂层材料和热界面材料。

1066406StewartThe lattice thermal conductivity is a fundamental thermal transport parameter that determines the utility of materials for specific thermal management applications. Accurate theoretical modeling of the lattice thermal conductivity is essential to numerous fields including microelectronics cooling, thermoelectrics, and even planetary science. The goal of this collaborative research effort between Boston College and Cornell University will be to implement a theoretical approach to calculate the lattice thermal conductivity of crystalline and alloyed materials from first principles. A central feature of this approach is that it has no adjustable parameters.The Cornell site will focus on calculating ab initio harmonic and, where required, anharmonic interatomic force constants (IFCs) for the materials and structures to be investigated. These calculations will be based on density functional perturbation theory. The IFCs are required inputs for phonon dispersions, phonon density of states, and phonon thermal transport calculations from which the lattice thermal conductivity is obtained. The materials to be studied in this project include lead chalcogenides, I-V-VI2 semiconductors, and nanoparticle-in-alloy-structures.The first principles approach has already demonstrated excellent agreement with measured high thermal conductivities of group IV semiconductors. The materials to be studied in this project are unified by their exceptionally low thermal conductivities and therefore provide an excellent test of the robustness of the theory. The measured thermal properties of many of these materials are well characterized and will provide an important check of our calculated adjustable parameter-free results. Good agreement with measured data would further validate the predictive capability of this state-of-the-art theory in studying and understanding thermal transport and the lattice thermal conductivity in a wide range of materials for many thermal management applications.Intellectual merit: Current theories of the lattice thermal conductivity of materials are typically based on either highly parameterized relaxation time approximations or on purely classical molecular dynamics calculations. The rigorous first principles theory proposed here has no adjustable parameters and incorporates fully the quantum mechanical phonon scattering processes. It therefore could provide currently unavailable predictive power to support ongoing and future experimental studies of thermal transport in materials, as well as contributing to the development of new highly efficient materials engineered for desired thermal management applications.Broader impacts: The project will provide training for one postdoctoral researcher at Cornell University and one doctoral graduate student at Boston College. In addition, several undergraduates including those from underrepresented groups will participate through NSF REU programs at both the Boston College and Cornell sites. The computational tools to be developed during this project will be incorporated into the publicly available computing library of the Cornell Nanoscale Science and Technology Facility (CNF). The activity will also benefit society by aiding in the development of new materials with desired thermal transport properties. This will facilitate technological breakthroughs that may lead to the next generation of thermoelectric materials, thermal barrier coating materials, and thermal interface materials.