Electronic Structure and Excitation Spectra of Magnetic Materials within First-Principles Many-Body Perturbation Theory

我们开发了一种基于多体微扰理论的计算方法，使磁性材料的电子结构和激发谱的第一性原理计算成为可能。为此，我们扩展了电子自能的gw近似，以考虑电子系统的自旋极化。在这个水平上，自旋能仍然是为每个自旋通道单独计算的。作为一个主要目标，我们然后通过以耦合两个自旋通道的散射矩阵的形式包括适当的顶点修正来处理可能的自旋翻转过程。该实现基于全电子方法，避免了假势的使用。该方法可以获得的关键量是准粒子带结构，包括两个自旋通道之间的交换分裂，以及谱函数，除了主要的准粒子峰外，还以卫星共振的形式显示了额外的集体激励。激发的寿命可以由复准粒子能量的虚部得到。理论方法是通用的，如果自旋极化起重要作用，可以应用于磁性体材料，表面和纳米结构。

We develop a computational method based on a many-body perturbation theory to enable first-principle calculations of the electronic structure and excitation spectra of magnetic materials. To this effect we extend the GW-approximation for the electronic self-energy to take the spin polarisation of the electron system into account. At this level the self-energy is still calculated separately for each spin channel. As a major goal, we then treat possible spin-flip processes by including appropriate vertex corrections in the form of a scattering matrix that couples the two spin channels. The implementation is based on an all-electron approach and avoids the use of pseudopotentials. Key quantities that can be obtained with this method are the quasi-particle band structure, including the exchange splitting between the two spin channels, as well as the spectral function, which in addition to the main quasi-particle peaks also shows additional collective excitations in the form of satellite resonances. The lifetime of the excitations can be obtained from the imaginary part of the complex quasi-particle energies. The theoretical approach is universal and can be applied to magnetic bulk materials, surfaces and nanostructures if spin polarisation plays an important role.