Recently a novel approach to find approximate exchange-correlation functionals in density-functional theory (DFT) was presented (U. Mordovina et. al., JCTC 15, 5209 (2019)), which relies on approximations to the interacting wave function using density-matrix embedding theory (DMET). This approximate interacting wave function is constructed by using a projection determined by an iterative procedure that makes parts of the reduced density matrix of an auxiliary system the same as the approximate interacting density matrix. If only the diagonal of both systems are connected this leads to an approximation of the interacting-to-non-interacting mapping of the Kohn-Sham approach to DFT. Yet other choices are possible and allow to connect DMET with other DFTs such as kinetic-energy DFT or reduced density-matrix functional theory. In this work we give a detailed review of the basics of the DMET procedure from a DFT perspective and show how both approaches can be used to supplement each other. We do so explicitly for the case of a one-dimensional lattice system, as this is the simplest setting where we can apply DMET and the one that was originally presented. Among others we highlight how the mappings of DFTs can be used to identify uniquely defined auxiliary systems and auxiliary projections in DMET and how to construct approximations for different DFTs using DMET inspired projections. Such alternative approximation strategies become especially important for DFTs that are based on non-linearly coupled observables such as kinetic-energy DFT, where the Kohn-Sham fields are no longer simply obtainable by functional differentiation of an energy expression, or for reduced density-matrix functional theories, where a straightforward Kohn-Sham construction is not feasible.
Local Potential Functional Embedding Theory: A Self-Consistent Flavor of Density Functional Theory for Lattices without Density Functionals
最近提出的Householder变换密度矩阵功能嵌入理论（Ht-DMFET）[Sekaran等人，Phys. Rev. B 104，035121（2021）]，其等价于（但形式上比）非相互作用情况下的密度矩阵嵌入理论（DMET），从密度泛函理论（DFT）的角度重新审视。本文推导了一种适用于含单一杂质的一维Hubbard晶格的密度泛函型HT-DMFET。在已有的密度泛函近似的基础上，提出并实现了局域势泛函嵌入理论。尽管LPFET在低密度区的表现优于Ht-DMFET，特别是当电子相关性较强时，但这两种方法都无法描述密度驱动的Mott-Hubbard跃迁。这些结果结合我们的正式精确的密度泛函嵌入理论表明，一个单一的静态嵌入杂质可以在原则上描述的间隙开口，提供的互补相关势（描述的嵌入集群与其环境的相互作用，这是简单地忽略在HT-DMFET和LPFET）表现出导数不连续（DD）在半填充。将LPFET扩展到多个杂质（这将使得能够规避DDs的建模）及其推广到量子化学哈密顿量的工作留给未来的工作。
Force Balance Approach for Advanced Approximations in Density Functional Theories
我们提出了一个系统的和建设性的方法来确定交换相关势的密度泛函理论，包括矢量势。该方法不依赖于能量或作用泛函。相反，它是基于电流量的运动方程（力平衡方程），是可行的，在基态和时间相关的设置。除了可微性和因果关系问题外，这避免了轨道相关泛函的优化有效势过程。我们为不同的密度泛函理论提供了简单的交换型近似，对于均匀系统和没有外部矢量势的交换仅局部密度和Slater X $α$近似。
Tensor network influence functionals in the continuous-time limit: connections to quantum embedding, bath discretization, and higher-order time propagation
