Merging GW and dynamical mean-field theory

基于局域密度近似(LDA)和动力学平均场理论(DMFT)的材料计算方法是向前迈出的一大步，因为它包含了强电子关联效应。然而，对于真正的无参数从头计算，仍然存在两个严重的缺陷：(I)屏蔽库仑相互作用通常被认为是LDA+DMFT中的一个可调参数；(Ii)所谓的重复计数问题，例如，很难确定已经在LDA水平上考虑的电子关联。虽然人们可以通过受限的LDA计算来缓解这些问题，但在概念上更可取的和定义良好的方法是用GW取代LDA。该项目的主要目标是实施GW+DMFT方法，并向科学界提供一揽子计划。我们将在GW+DMFT从物理角度来看更优越的情况下应用这种方法，即如果交换除了强电子关联之外还很重要。我们将研究半导体，在这些半导体中，GW对带隙的估计比LDA好得多，如果存在过渡金属，也需要包括强相关性。第二种应用是新型超导体，如铜酸盐和铁锡化合物，其中过渡金属d电子与O或As p空穴之间的交换作用可能是重要的。

Material calculations on the basis of the local density approximation (LDA) plus dynamical mean field theory (DMFT) approach represent a major step forward, since strong electronic correlation effects are included. For truly parameter-free ab initio calculations, however, two severe shortcomings persist: (i) the screened Coulomb interaction is usually considered to be an adjustable parameter in LDA+DMFT and (ii) the so-called double counting problem, e.g., it is difficult to determine the electronic correlations already accounted for on the LDA level. While one might mitigate these problems by constrained LDA calculations, a conceptionally preferable and well-defined approach is to substitute LDA by GW. The main goal of this project is to implement the GW+DMFT approach and to make the program package available to the scientific community. We will apply this approach in cases where GW+DMFT is superior from a physical point of view, i.e., if the exchange is important besides strong electronic correlations. We will study semiconductors where GW estimates band gap values much better than LDA and where, if transition metals are present, strong correlations need to be included as well. A second application are novel superconductors such as cuprates and iron pnictides, where the exchange interactions between transition metal d electrons and O or As p holes might be important.