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arXiv 1109.0158cond-mat.str-el
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精确对角化动力学平均场论中的温度和熔池尺寸

Temperature and bath size in exact diagonalization dynamical mean field theory

Ansgar Liebsch, Hiroshi Ishida

摘要:

DMFT结合有限T精确对角化是描述强关联材料电子性质的方法之一。由于希尔伯特空间的快速增长,用于表示无限晶格的有限浴的大小受到严格限制。鉴于人们对过渡金属氧化物、高温铜酸盐、铁基磷属元素化物、有机晶体等中多轨道和多位库仑关联效应的兴趣日益增加,适当的是探索温度和浴尺寸的范围,其中ED提供各种系统性质的准确结果。熔池必须足够大,以获得足够密集的能级间距,从而可以获得有用的光谱信息,特别是接近费米能级的光谱信息。为了将晶格格林函数充分投影到有限浴上,温度的选择至关重要。ED DMFT中这两个关键成分的作用进行了讨论,各种各样的系统,以建立这种方法的适用性域。三个标准被用来说明结果的准确性:(i)收敛的自能浴大小,(ii)质量的离散化浴格林函数,及(iii)通过CTQMC DMFT获得的互补结果的比较。这些材料包括各种三轨道和五轨道系统,以及二维三角形、正方形和蜂窝晶格的单带哈伯德模型,其中非局部库仑相关性很重要。从这些例子中得出的主要结论是,大量的相关轨道或位点需要较少的浴水平。下至5至10 meV的温度(对于典型的带宽W=2 eV),每个相关杂质轨道或位置的两个浴水平通常是足够的。

英文摘要:

DMFT combined with finite-T exact diagonalization is one of the methods to describe electronic properties of strongly correlated materials. Because of the rapid growth of the Hilbert space, the size of the finite bath used to represent the infinite lattice is severely limited. In view of the increasing interest in the effect of multi-orbital and multi-site Coulomb correlations in transition metal oxides, high-Tc cuprates, iron-based pnictides, organic crystals, etc., it is appropriate to explore the range of temperatures and bath sizes in which ED provides accurate results for various system properties. The bath must be large enough to achieve a sufficiently dense level spacing, so that useful spectral information can be derived, especially close to the Fermi-level. For an adequate projection of the lattice Green's function onto a finite bath, the choice of the temperature is crucial. The role of these two key ingredients in ED DMFT is discussed for a wide variety of systems in order to establish the domain of applicability of this approach. Three criteria are used to illustrate the accuracy of the results: (i) the convergence of the self-energy with bath size, (ii) quality of the discretization of the bath Green's function, and (iii) comparisons with complementary results obtained via CTQMC DMFT. The materials comprise a variety of three- and five-orbital systems, as well as single-band Hubbard models for two-dimensional triangular, square and honeycomb lattices, where non-local Coulomb correlations are important. The main conclusion from these examples is that a larger number of correlated orbitals or sites requires a smaller number of bath levels. Down to temperatures of 5 to 10 meV (for typical band widths W=2 eV) two bath levels per correlated impurity orbital or site are usually adequate.

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