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

晶格导热系数是一个基本的热传输参数，它决定了材料在特定热管理应用中的效用。晶格导热系数的精确理论模型在微电子冷却、热电学甚至行星科学等众多领域都是必不可少的。波士顿学院和康奈尔大学的这项合作研究的目标将是实施一种理论方法，从第一性原理计算晶体和合金材料的晶格热导率。这种方法的一个主要特点是它没有可调整的参数。康奈尔大学的站点将专注于计算从头算谐和，如果需要的话，计算被研究材料和结构的非谐原子力常数(IFCs)。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必需的输入，从这些计算中可以得到晶格热导率。本项目研究的材料包括硫族铅化物、I-V-VI2半导体和合金纳米颗粒结构。第一性原理方法已经证明与测量的IV族半导体的高导热系数具有很好的一致性。本项目中要研究的材料因其极低的导热系数而统一，因此为该理论的稳健性提供了极好的测试。这些材料中的许多材料的测量的热性能都得到了很好的表征，并将为我们计算的可调无参数结果提供重要的检验。与测量数据的良好一致性将进一步验证这一最先进的理论在研究和理解各种材料中的热输运和晶格热导率方面的预测能力，以用于许多热管理应用。智力优势：当前的材料晶格热导率理论通常基于高度参数化的驰豫时间近似或纯经典的分子动力学计算。本文提出的严格第一原理理论没有可调参数，完全包含了量子力学声子散射过程。因此，它可以提供目前无法获得的预测能力，以支持正在进行的和未来的材料热传输实验研究，并有助于为所需的热管理应用设计的新的高效材料的开发。广泛影响：该项目将为康奈尔大学的一名博士后研究员和波士顿学院的一名博士后研究生提供培训。此外，几名本科生，包括那些来自代表不足的群体的学生，将通过波士顿学院和康奈尔大学的NSF REU计划参加。将在该项目期间开发的计算工具将被纳入康奈尔纳米科学和技术设施(CNF)的公开可用的计算库。该活动还将帮助开发具有所需热传输性能的新材料，从而造福社会。这将促进可能导致下一代热电材料、热障涂层材料和热界面材料的技术突破。

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.