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arXiv 2104.09207cond-mat.str-elcond-mat.mtrl-scicond-mat.supr-con
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Su-Schrieffer-Heeger模型

Downfolding the Su-Schrieffer-Heeger model

Arne Schobert, Jan Berges, Tim Wehling, Erik van Loon

摘要:

电荷密度波负责原子的破缺位移和伴随的电子结构变化。线性响应理论,特别是密度泛函微扰理论,提供了一种方法来研究位移对总能量和电子结构的影响,基于一个单一的从头计算。在下折方法中,电子系统被减少到更少数量的频带,允许在这些频带上并入额外的相关性和环境效应。然而,这种下折模型的物理内容及其潜在的局限性并不总是显而易见的。在这里,我们研究的势能景观和电子结构的苏-Schrieffer-Heeger(SSH)模型,其中所有相关的数量可以分析评估。我们比较了在任意位移的精确结果与图解微扰理论在完整的模型和向下折叠的有效单带模型,这给了一个有益的洞察向下折叠的属性。在一个向下折叠的模型中,势能景观的精确重建是可能的,这需要一个动态的电子-双声子相互作用。原子位移时的带的色散也被正确地发现,其中通过构造的下折模型仅捕获目标空间中的光谱权重。在SSH模型中,电子-声子耦合机制仅涉及低能带和高能带之间的杂化,这限制了下折模型的计算效率增益。

英文摘要:

Charge-density waves are responsible for symmetry-breaking displacements of atoms and concomitant changes in the electronic structure. Linear response theories, in particular density-functional perturbation theory, provide a way to study the effect of displacements on both the total energy and the electronic structure based on a single ab initio calculation. In downfolding approaches, the electronic system is reduced to a smaller number of bands, allowing for the incorporation of additional correlation and environmental effects on these bands. However, the physical contents of this downfolded model and its potential limitations are not always obvious. Here, we study the potential-energy landscape and electronic structure of the Su-Schrieffer-Heeger (SSH) model, where all relevant quantities can be evaluated analytically. We compare the exact results at arbitrary displacement with diagrammatic perturbation theory both in the full model and in a downfolded effective single-band model, which gives an instructive insight into the properties of downfolding. An exact reconstruction of the potential-energy landscape is possible in a downfolded model, which requires a dynamical electron-biphonon interaction. The dispersion of the bands upon atomic displacement is also found correctly, where the downfolded model by construction only captures spectral weight in the target space. In the SSH model, the electron-phonon coupling mechanism involves exclusively hybridization between the low- and high-energy bands and this limits the computational efficiency gain of downfolded models.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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