Atomistic Design of Thermal and Electrical Transport in Materials with Dislocations: From High Power Electronics to Thermoelectrics

位错控制材料合成的最新进展表明，纳米材料中的工程位错的新的可能性。为了利用这些进展并指导具有工程位错的材料的合成，需要位错-输运性质关系的精确模型。我们提出的研究，以推进原子计算技术和理论概念，需要理解和预测的结构输运性质的材料空间。扩展的应变场和动态颤动的位错，以及它们对电子性质的影响是计算易处理的基于密度泛函理论的紧束缚（DFTB）方法。为了使预测在热域中，我们建议耦合DFTB与（i）多体非平衡绿色的函数方法的量子声子输运与原子间的非谐性，（ii）一个平衡的目标分子动力学方法计算声子带结构，寿命和群速度计算，和（iii）波包方法研究声子的传播和散射。 我们将应用开发的工具来研究如何赋予最大或最小的晶格热导率，同时保持大的载流子迁移率和塞贝克系数在散装，一维和二维材料。(i)在散装材料中的位错的模拟将针对实验观察到的热电品质因数的显着改善的理解与低固有的热导率和嵌入密集的位错阵列沿着晶界的材料。(ii)纳米线是实现高热电性能的有吸引力的纳米结构，但位于其核心的位错的影响是未知的。 纳米线存储位错的模拟旨在揭示一个新的重要机制（声子位错散射），提高热电优值。(iii)二维材料对于纳米电子器件是非常重要的，但是位于其晶界处的位错阵列（固有的扩展缺陷）容易引起不必要的效应，如严重的自加热。调查将揭示位错阵列模型，提供最佳的电荷传输与最小的热量产生在晶界。

Recent advances in material synthesis controlled by dislocations suggest the novel possibility of engineering dislocations in nanomaterials. To leverage these advances and guide the synthesis of materials with engineered dislocations, accurate models for the dislocation-transport property relationship are needed. We propose research to advance the atomistic computational techniques and theoretical con-cepts needed to understand and predict the structure-transport properties across the material space. The extended strain fields and dynamic fluttering of the dislocations, and their impact on electronic properties are computationally tractable with the density functional theory based tight-binding (DFTB) method. To enable predictions in the thermal domain, we propose to couple DFTB with (i) a many-body non-equilibrium Green’s-function approach for quantum phononic transport with inter-atomic anharmonicity, (ii) an equilibrium objective molecular dynamics method for computing phonon band structure, lifetime, and group velocity calculations, and (iii) wave packet methods for studying phonon propagation and scattering. We will apply the developed tools to investigate ways to impart maximal or minimal lattice ther-mal conductivity while maintaining a large charge carrier mobility and Seebeck coefficient in bulk, one-dimensional, and two-dimensional materials. (i) Simulations of dislocations in bulk materials will target an understanding of the experimentally observed dramatic improvements in the thermoelectric figure of merit in materials with low intrinsic thermal conductivities and em-bedded dense dislocation arrays along grain boundaries. (ii) Nanowires are attractive nanostructures for achieving high thermoelectric performances, but the impact of dislocations located at their core is unknown. Simulations of nanowires storing dislocations aim to uncover a new important mechanism (phonon-dislocation scattering) for boosting the thermoelectric figure of merit. (iii) Two-dimensional materials are of tremendous importance for nanoelectronics devices, but the arrays of dislocations located at their grain boundaries (inherent extended defects) are prone to induce unwanted effects like severe self-heating. Investigations will un-cover dislocations array models that deliver optimal electrical charge transport with minimum heat generation at the grain boundaries.