Ankudinov A L, Rehr J J
Department of Physics, Box 351560, University of Washington, Seattle, WA 98195, USA.
J Synchrotron Radiat. 2003 Sep 1;10(Pt 5):366-8. doi: 10.1107/s0909049503009130. Epub 2003 Aug 28.
A major goal of theoretical simulations of X-ray absorption fine structure (XAFS) is to provide calculations for the interpretation and analysis of experimental data in terms of geometrical and electronic information. The extended region or EXAFS (50-2000 eV above an absorption edge) contains geometric information about the pair distribution function, i.e. distances to the nearest neighbors and their orientation. The theory of EXAFS is now well understood and has been recently reviewed [Rehr & Albers (2000). Rev. Mod. Phys. 72, 621-654]. The near-edge region (0-50 eV above the edge) or X-ray absorption near-edge structure (XANES) probes the states just above the Fermi level, and contains important electronic information, e.g. the electronic density of states (DOS). This data can be used to obtain the number of electrons or holes in the electronic configuration and spin and orbital moments on a particular atom via sum rules. XANES calculations with our ab initio code FEFF8 [Ankudinov et al. (1998). Phys. Rev. B, 58, 7565-7576] usually give semi-quantitative agreement with experiment, and permits the interpretation of XANES in terms of DOS. However, fully quantitative calculations remain a challenge. Several effects still need to be considered to treat the XANES region. These include non-spherical parts of the scattering potential and many-body effects such as multi-electron excitations, core-hole effects and local field effects (screening of the X-ray field).
X射线吸收精细结构（XAFS）理论模拟的一个主要目标是根据几何和电子信息，为实验数据的解释和分析提供计算。扩展区域即扩展X射线吸收精细结构（EXAFS，在吸收边以上50 - 2000电子伏特）包含有关对分布函数的几何信息，即到最近邻原子的距离及其取向。EXAFS理论现在已被充分理解，并且最近已有综述[Rehr & Albers（2000年）。《现代物理评论》72卷，621 - 654页]。近边区域（在吸收边以上0 - 50电子伏特）或X射线吸收近边结构（XANES）探测费米能级以上的态，并包含重要的电子信息，例如态密度（DOS）。该数据可用于通过求和规则获得特定原子电子构型中的电子或空穴数量以及自旋和轨道矩。使用我们的从头算代码FEFF8 [Ankudinov等人（1998年）。《物理评论B》，58卷，7565 - 7576页]进行的XANES计算通常与实验给出半定量的一致性，并允许根据态密度解释XANES。然而，完全定量的计算仍然是一个挑战。处理XANES区域仍需考虑几种效应。这些效应包括散射势的非球形部分以及多体效应，如多电子激发、芯孔效应和局部场效应（X射线场的屏蔽）。
