Realistic theory of electronic correlations in nanoscopic systems

纳米系统中电子关联的现实理论

• 批准号: 240207043
• 负责人: Professor Dr. Giorgio Sangiovanni
• 金额: --
• 依托单位: I. Institut für Theoretische Physik
• 依托单位国家: 德国
• 项目类别: Research Units
• 财政年份: 2013
• 资助国家: 德国
• 起止时间: 2012-12-31 至 2017-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/240207043?language=en
• 关键词: Realistic; theory; electronic; correlations; nanoscopic

The central goal of this project is to build a stable, flexible and user-friendly computational scheme with predictive power on the electronic and magnetic properties of nanostructures with correlated electrons. This scheme will provide direct links to experiments of scanning tunneling microscopy (STM), x-ray absorption spectroscopy (XAS), x-ray circular magnetic dichroism (XMCD), photoelectron spectroscopy (PES) and electron transport in nanostructures. To this end, method developments will be performed along with applications to the example systems of transition-metal clusters on surfaces, two-site Kondo systems, nanoscopic Mott systems as well as complex organic and metal-organic molecules coupled to metallic surfaces.Correlated nano systems are highly responsive to external perturbations, such as pressure, temperature, or strain and are therefore appealing in the context of new applications and novel physical effects but they are theoretically very demanding and pose several challenges: First, it is prohibitively hard to treat on an equal footing the realistic electronic-structure of nanostructures and the interaction effects among several sites (or impurities) with rich multiplet structures. Moreover, the competition between the screening effects of the leads or the surface and non-local correlation effects resulting from the presence of several coupled impurities as well as the possibility of strong non-local Coulomb interactions are open problems. Finally, experiments in nano science frequently base on local probe and nano contact techniques. Thus, a new theory capable of simulating realistic experimental spectra reliably has to be established. To address these challenges, we will combine ab-initio methods such as density functional theory (DFT) and many-body approaches such as dynamical mean field theory (DMFT) and its diagrammatic extensions. To extend the successful combination of these two classes of theories (the so-called “LDA+DMFT” approach) from bulk materials with correlated electrons to nanoscopic systems a number of additional issues has to be solved. Firstly, DFT calculations and their interfacing with DMFT are more difficult for nanoscopic systems than for bulk materials, as sizable structural relaxations as well as coupling of many inequivalent atoms to substrates or leads must be taken into account at the same time. From the many-body point of view the main obstacle lies in taking non-local correlations properly into account. In three-dimensional bulk materials one can – under some circumstances – apply the DMFT assuming a local self-energy. However, the window of validity of such approximation is much narrower in nanoscopic systems. All of these problems will be addressed in the time-frame of this project by developing a reliable and stable theory of correlated nano systems.

该项目的中心目标是建立一个稳定、灵活和用户友好的计算方案，对具有相关电子的纳米结构的电子和磁性特性具有预测能力。该方案将提供与扫描隧道显微镜（STM）、X射线吸收光谱（XAS）、X射线圆磁二色性（XMCD）、光电子能谱（PES）和纳米结构电子传输实验的直接联系。为此，方法开发将与表面过渡金属簇的示例系统、两位点近藤系统、纳米级莫特系统以及耦合到金属表面的复杂有机和金属有机分子的应用一起进行。相关的纳米系统对压力、温度或应变等外部扰动高度敏感，因此在新应用和新颖的背景下很有吸引力 物理效应，但它们在理论上要求非常高，并带来了一些挑战：首先，在平等的基础上处理纳米结构的真实电子结构以及具有丰富多重结构的多个位点（或杂质）之间的相互作用效应是极其困难的。此外，引线或表面的屏蔽效应与由于多种耦合杂质的存在而导致的非局域相关效应之间的竞争以及强非局域库仑相互作用的可能性也是悬而未决的问题。最后，纳米科学实验经常基于局部探针和纳米接触技术。因此，必须建立一种能够可靠地模拟现实实验光谱的新理论。为了应对这些挑战，我们将结合密度泛函理论 (DFT) 等从头算方法和动态平均场理论 (DMFT) 及其图解扩展等多体方法。为了将这两类理论（所谓的“LDA+DMFT”方法）的成功组合从具有相关电子的块体材料扩展到纳米系统，还必须解决许多其他问题。首先，DFT 计算及其与 DMFT 的接口对于纳米系统比对于块体材料更困难，因为必须同时考虑相当大的结构松弛以及许多不等价原子与基底或引线的耦合。从多体的角度来看，主要障碍在于正确考虑非局部相关性。在三维散装材料中，在某些情况下，我们可以假设局部自能应用 DMFT。然而，这种近似的有效性窗口在纳米级系统中要窄得多。所有这些问题都将在该项目的时间内通过开发可靠且稳定的相关纳米系统理论来解决。