First-principles calculations of x-ray absorption near edge structure and energy loss near edge structure: present and future.

Computational methods for theoretical x-ray absorption near edge structure (XANES) and energy loss near edge structure (ELNES) are classified into a few groups. Depending on the absorption (or excitation) edge, required accuracy and desired information, one needs to select the most suitable method. In this paper, after providing a map of available computational methods, some examples of first-principles calculations of XANES/ELNES for selected wide gap materials are given together with references. For ZnO, for example, experimental spectra at three edges, Zn K, L(3), and O K, including their orientation dependence, are well reproduced by the supercell calculations with a core hole. Good agreement between theoretical and experimental spectra of ZnO alloys can also be seen. Theoretical fingerprints are satisfactorily obtained in this way. However, there are remaining issues beyond 'good agreements' which need to be solved in the future.