Speaker
Description
X-ray absorption near-edge structure (XANES) spectroscopy is a widely used tool to determine structural, chemical, and electronic properties of finite and crystalline systems alike. Due to the localization of the excited core states, XANES is an element- and site-specific probe of the electronic environment of the absorbing atom. Complementing these experiments with accurate first-principles studies offers a comprehensive picture of the electronic structure of materials.
Here, we present an all-electron, many-body approach to describe core excitations in solids from first principles, which is implemented in the open-source, all-electron full-potential code exciting [1,2]. Starting from the electronic structure obtained from density-functional theory, which includes an explicit treatment of core states, we obtain absorption spectra in the framework of many-body perturbation theory through the solution of the Bethe-Salpeter equation [3]. In this approach, the effects of the interaction between the excited electron and the core hole, screened by the surrounding many-electron system, are included.
As exemplary cases, we present core spectra of the oxides CaO and TiO$_2$, where we consider excitations from the Ca 2p and Ti 1s states. In both examples, we discuss the role of the electron-core hole correlation and analyze the excitations, revealing the contributions of specific bands and regions of the Brillouin zone to the final states. Our results are in good agreement with available experimental data.
References
[1] C. Vorwerk, C. Cocchi, and C. Draxl, Phys. Rev. B 95, 155121 (2017).
[2] A. Gulans et al., J. Phys. Condens. Matter 26, 363202 (2014).
[3] G. Onida, L. Reining, and A. Rubio, Rev. Mod. Phys. 74, 601 (2002).
