Full-Potential Multiple Scattering Theory And Its Application In Nano-structured Systems

X-ray Absorption Near-Edge Structure (XANES) is an invaluable tool to study the electronic structure of and local atomic structure around selected elements in materi-als. However, to extract such information, a good theoretical tool that has predictive performances indispensable. Multiple Scattering theory (MST) has been very widely applied to the computation of XANES of various materials. However, due to the use of the Muffin-Tin (MT) approximation, the conventional MST cannot properly describe a great number of physical systems, ranging from open lattices to molecular systems, to surfaces and interfaces. To overcome these barriers, people have to go beyond the MT approximation to the full-potential multiple scattering theory (FP-MST). In this article, the author will summarize previous developments of FP-MST and give a detailed de-scription of a recently developed FP-MST with space-filling cells (K. Hatada et al,2007, 2010). Some other developments and theoretical limits of MST are also discussed.The author’s work focuses on theoretical development of FP-MST and related ap-plications in XANES of nanostructured systems. The research activities are summarized in the following:1. The author developed an interface program, called ES2MS, to obtain the all-electron self-consistent potentials and charge densities for FPMS program, which im-plements Hatada’s FP-MST, from a plane-wave ab initio code-VASP. ES2MS program solves Poisson equation to construct the all-electron potential inside augmented spheres on the radial mesh, from the pseudo potential and all-electron charge density generated by VASP code.2. With the newly developed ES2MS interface and FPMS program, the author calculated C and O K-edge X-ray absorption spectra of graphene and graphene oxide with self-consistent charge density and potential. Compared to standard multiple scat-tering (MS) calculations in the MT approximation, our results agree much better with experimental data. The effects of various structural modifications, containing stacking of layers, edge structure and adsorption of oxygen, on the graphene spectra are well reproduced.3. The author developed a new, efficient algorithm for the scattering matrix inver-sion, which is the most time-consuming process in MS calculations of not very small systems, and has implemented it into FPMS program. The new method strongly reduces the computation time, typically by a factor of 20-30, without significant loss of accu-racy. The algorithm is based on a partitioning of the scattering matrix by a particular orbital angular moment and approximate submatrices to simpler forms.4. The author has been working on implementation of a "complete" real-space multiple scattering approach in MsSpec program to the Electron Energy Loss Spec-troscopy, which gives similar information to X-ray Absorption Spectroscopy, where we have considered the multiple scattering effects on the incoming and outgoing elec-trons which are neglected in other codes.