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为纳米材料的工程位错提供了新的可能性。为了利用这些进展并指导具有工程位错的材料的合成，需要准确的位错-输运性质关系模型。我们建议研究推进原子计算技术和理论概念，以理解和预测跨材料空间的结构-输运性质。基于密度泛函理论的紧密结合（DFTB）方法可以计算处理位错的扩展应变场和动态颤振及其对电子性能的影响。为了实现热域的预测，我们建议将DFTB与(i)具有原子间非谐性的量子声子输运的多体非平衡格林函数方法相结合，（ii）用于计算声子带结构、寿命和群速度计算的平衡客观分子动力学方法，以及（iii）用于研究声子传播和散射的波包方法。我们将应用开发的工具来研究如何在保持大块、一维和二维材料的大载流子迁移率和塞贝克系数的同时，赋予最大或最小的晶格热导率。(i)块状材料中位错的模拟将以理解实验观察到的具有低固有热导率和沿晶界嵌入密集位错阵列的材料的热电优值的显着改善为目标。（ii）纳米线是实现高热电性能的极具吸引力的纳米结构，但其核心位错的影响尚不清楚。纳米线存储位错的模拟旨在揭示一种新的重要机制（声子位错散射），以提高热电性能。（iii）二维材料对于纳米电子器件非常重要，但是位于其晶界的位错阵列（固有扩展缺陷）容易引起严重的自热等不良影响。研究将揭示位错阵列模型，提供最佳的电荷传输，在晶界产生最小的热量。

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.