Recent progress in understanding thermal transport in complex crystals has highlighted the prominent role of heat conduction mediated by interband tunneling processes, which emerge between overlapping phonon bands (i.e. with energy differences smaller than their broadenings). These processes have recently been described in different ways, relying on the Wigner or Green-Kubo formalism, leading to apparently different results which question the definition of the heat-current operator. Here, we implement a full quantum approach based on the Kubo formula, elucidating analogies and differences with the recently introduced Wigner or Green-Kubo formulations, and extending the description of thermal transport to the overdamped regime of atomic vibrations, where the phonon quasiparticle picture breaks down. We rely on first-principles calculations on complex crystals with ultralow conductivity to compare numerically the thermal conductivity obtained within the aforementioned approaches, showing that at least in the quasiparticle regime the differences are negligible for practical applications.
Thermal expansion in carbon nanotubes and graphene: nonequilibrium Green's function approach
采用非平衡格林函数方法研究了单壁碳纳米管和石墨烯的热膨胀系数。结果表明，在T=0 K时，原子偏离平衡位置约1%，这是量子零点运动和非线性相互作用相互作用的结果。从不同振动模式之间的竞争角度对不同尺寸单壁碳纳米管的热膨胀系数进行了研究和分析。由于这种竞争，轴向CTE在整个温度范围内是正的，而径向CTE在低温下是负的。在石墨烯中，CTE对衬底非常敏感。在没有基底的情况下，CTE在低温下具有大的负区域，在高温极限下具有非常小的值，并且在T=300 K下的CTE值是$-6\times 10^{-6}$ K $^{-1}$，其非常接近最近的实验结果，$-7\times 10^{-6}$ K $^{-1}$（Nat.Nanotechnol. \textbf{10}，1038（2009））。很弱的衬底相互作用（约为面内相互作用的0.06%）可以大大减小负CTE区域，并大大提高CTE值。当衬底相互作用足够强时，热膨胀系数在整个温度范围内均为正值，高温下的饱和值达到$2.0\times 10^{-5}$ K $^{-1}$。
Heat-current filtering for Green-Kubo and Helfand-moment molecular dynamics predictions of thermal conductivity: Application to the organic crystal $β$-HMX
Efficient ab initio many-body calculations based on sparse modeling of Matsubara Green's function
本课堂讲稿回顾了最近提出的基于格林函数数据压缩的有效从头计算多体计算的稀疏建模方法。稀疏建模技术是基于一个紧凑的正交基，一个中间表示（IR）的基础上，时间和松原格林函数。基于IR基的稀疏采样方法可以有效地求解图解方程。我们描述了IR基的基本性质，稀疏采样方法及其在基于GW近似和Migdal-Eliashberg理论的从头计算中的应用。我们还描述了一个数值库的IR基础和稀疏采样方法，稀疏IR，并提供其示例代码。这份课堂讲稿是在日文评论文章的基础上做了重大修改[H. Shinaoka等人，Solid State Physics 56（6），301（2021）]。
Thermal boundary conductance across epitaxial ZnO/GaN interfaces: Assessment of phonon gas models and atomistic Green's function approaches for predicting interfacial phonon transport
我们目前的实验测量的热边界电导（TBC）从$77 - 500$ K跨隔离异质外延生长的ZnO薄膜在GAN衬底上。这些数据提供了一个评估的假设，驱动声子气体模型为基础的扩散失配模型（DMM）和原子格林函数（AGF）预测TBC的形式主义。我们的测量结果，与以前的实验数据相比，表明TBC可以受到长波长，区域中心模式的界面一侧的材料，而不是在DMM假设的“振动失配”的概念，这种分歧是在高温下明显。在室温下，我们测量ZnO/GAN TBC为$490\lbrack +150, -110\rbrack$ MW m $^{-2}$ K $^{-1}$。DMM和AGF之间的分歧和这些升高的温度的实验数据表明，不可忽略的贡献，从其他模式有助于TBC，不占在这些谐波形式主义的基本假设，如非弹性散射。考虑到这些ZnO/GAN界面的高质量，这些结果提供了一个宝贵的关键和定量评估的准确性的假设，在当前的计算方法的最先进的预测声子TBC跨界面。
Total energies from variational functionals of the Green function and the renormalized four-point vertex
We derive variational expressions for the grand potential or action in terms of the many-body Green function $G$ which describes the propagation of particles and the renormalized four-point vertex $Γ$ which describes the scattering of two particles in many-body systems. The main ingredient of the variational functionals is a term we denote as the $Ξ$ -functional which plays a role analogously to the usual $Φ$ -functional studied by Baym (G.Baym, Phys.Rev. 127, 1391 (1962)) in connection with the conservation laws in many-body systems. We show that any $Ξ$ -derivable theory is also $Φ$ -derivab…
Superior effect of edge relative to basal plane functionalization of graphene in enhancing polymer-graphene nanocomposite thermal conductivity-A combined molecular dynamics and Greens functions study
