ABSTRACT

Recent advances in fabrication techniques have enabled the development of materials sculpted at the nanoscale (~10 nm). These “nano-materials” could revolutionize thermal management technologies by providing novel ways to manipulate energy propagation in solids. Atomistic simulations are critical to forging this revolution, given their ability to describe a system’s dynamics on an atom by atom basis. This topical review focuses on nonequilibrium Green’s functions (NEGF) simulations to model vibrational energy propagation at the nanoscale. NEGF is an atomistic and purely quantum mechanical approach well-suited to compute thermal transport in spatially varying systems such as “nano-materials.” This review presents the NEGF methodology from a top-to-bottom perspective, focusing on the concepts behind the mathematical expressions. We start describing the implementation of NEGF that assumes harmonic interatomic potentials (h-NEGF) and some recent advances that distinguish the transport contributions by different polarizations. This review also discusses the less common implementation of NEGF that includes the anharmonic terms of the potentials (a-NEGF), outlining existing approximations and standing challenges. Our success in tackling these challenges will determine whether we will harness the full potential of NEGF to describe thermal transport from a quantum mechanical standpoint.

摘要

制造技术的最新进展使得能够开发雕刻成纳米级（〜10 nm）的材料。这些“纳米材料”可以通过提供新颖的方式来控制固体中的能量传播，从而彻底改变热管理技术。鉴于原子模拟能够逐个原子地描述系统动力学，因此它们对于推动这一革命至关重要。这篇专题综述的重点是非平衡格林函数（NEGF）模拟，以模拟纳米级的振动能量传播。NEGF是原子性的纯量子力学方法，非常适合在空间变化的系统（例如“纳米材料”）中计算热传输。这篇综述从上到下的角度介绍了NEGF方法论，重点介绍了数学表达式背后的概念。我们开始描述假设有谐波原子间电势（h-NEGF）的NEGF的实现以及一些通过不同极化区分传输贡献的最新进展。这篇综述还讨论了NEGF的较不常见的实现方式，其中包括势能的非调和项（a-NEGF），概述了现有的近似值和存在的挑战。我们在应对这些挑战方面的成功将决定我们是否将利用NEGF的全部潜力从量子力学的角度描述热传输。这篇综述还讨论了NEGF的较不常见的实现方式，其中包括势能的非调和项（a-NEGF），概述了现有的近似值和存在的挑战。我们在应对这些挑战方面的成功将决定我们是否将利用NEGF的全部潜力从量子力学的角度描述热传输。这篇综述还讨论了NEGF的较不常见的实现方式，其中包括势能的非调和项（a-NEGF），概述了现有的近似值和存在的挑战。我们在应对这些挑战方面的成功将决定我们是否将利用NEGF的全部潜力从量子力学的角度描述热传输。