超越累积量近似：Holstein系统单粒子格林函数的幂级数修正
Going Beyond the Cumulant Approximation: Power Series Correction to Single Particle Green's Function in Holstein System
摘要：
在单电子两轨道Holstein系统耦合到无色散玻色子的背景下，我们开发了一个通用的方法来校正单粒子格林函数使用幂级数校正（PSC）计划。然后，我们通过PSC方案概述了各种累积量近似的推导，并解释了它们背后的假设和近似。最后，我们计算和比较PSC谱函数与累积量和精确对角化谱函数，并阐明这个问题的三个制度-两个累积量解释和一个累积量失败。我们发现，在所有三个政权的光谱展宽的确切和PSC光谱函数匹配。
英文摘要：
In the context of a single electron two orbital Holstein system coupled to dispersionless bosons, we develop a general method to correct single particle Green's function using a power series correction(PSC) scheme. We then outline the derivations of various flavors of cumulant approximation through the PSC scheme and explain the assumptions and approximations behind them. Finally, we compute and compare PSC spectral function with cumulant and exact diagonalized spectral functions and elucidate three regimes of this problem - two that cumulant explains and one where cumulant fails. We find that the exact and the PSC spectral functions match within spectral broadening across all three regimes.
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