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光谱的第一性原理计算。为此，我们扩展GW近似的电子自能考虑到自旋极化的电子系统。在这个水平上，自能仍然是为每个自旋通道单独计算的。作为一个主要目标，我们然后治疗可能的自旋翻转过程，包括适当的顶点校正的形式的散射矩阵耦合的两个自旋通道。该实现是基于一个全电子的方法，避免使用赝势。可以用这种方法获得的关键量是准粒子能带结构，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，还显示了以卫星共振形式的额外集体激发。激发态的寿命可以从复准粒子能量的虚部得到。理论方法是通用的，可以应用到磁性体材料，表面和纳米结构，如果自旋极化起着重要的作用。

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.