FEFF - 谱学多重散射计算软件

FEFF是自洽的多重散射从头计算XAS谱和电子结构的软件包。用于同时计算X射线吸收光谱和电子结构。输出扩展的X射线吸收精细结构（EXAFS），X射线吸收光谱（XAS）的全多次散射计算以及投影的局部密度（LDOS）。光谱边缘结构附近的X射线吸收（XANES），X射线自然和磁性圆二色性（XNCD和XMCD），自旋化X射线吸收光谱（SPXAS和SPEXAFS），非共振X射线光谱（XES），X射线散射幅度（Thomson）和电子能量损失谱（EELS）。该代码产生现代XAFS分析代码中使用的散射振幅和相位，以及属性。

FEFF 9：新版本是FEFF9（版本9.6）

FEFF 9 具有新功能和选项。有几个可以用FEFF 9计算的新的光谱，电子能量损失谱（EELS）和非共振非弹性X射线散射（NRIXS）。另外，还有改进。这些; 

（1）从头开始的 Debye-Waller因子;

（2）非弹性损失的治疗; 

（3）核心 - 空穴相互作用的改进处理; 

（4）用格林函数的k空间计算更地处理结晶体系。  

（5）利用基于自洽的球型MT散射势的实空间Green函数方法, 计算中考虑了polarization dependence, core-hole efects,and local field corrections,et al.

（6）FEFF9增加了倒空间计算(周期边界条件)

FEFF9附带JFEFF GUI。

FEFF能够提供如下的计算：

- 散射振幅: effective scattering amplitude；x-rayelastic scattering amplitude f = f0+f’+if ’’, including Thomson and anomalous parts

- 相移函数: Ø，effective scattering phase shift

- 平均自由程: λ，mean free path

- 初始路径长：R0

- Daybed-Waller因子: σ

- feffnnnn:

- chi :

- …..

FEFF9的模块结构

• 输入、输出处理

• 原子势计算

• 嵌入的原子势计算

• 屏蔽效应计算

• ldos计算

• 截面和相移函数计算

• 全多重散射计算

• 求GT的迹

• 路径计算

• 计算散射振幅和XAFS参数

• 计算指定的谱

• 计算多电子激发

• 计算eels

FEFF 8：

FEFF 8 通过自我的电势计算来提供电荷转移和更的费米能级估计，改进了FEFF的版本。它还多次散射计算，以XANES计算，其中多次散射扩展可能无法收敛。FEFF 8可输出角动量投影状态密度，x射线发射光谱和x射线散射振幅。FEFF 8.40的改进简化了依赖于自旋的计算，并且可以对核心孔和局部场效应的改进处理。FEFF8现在JEFEFF，FEFF 8.4的图形前端。 

【英文介绍】

FEFF is an automated program for ab initio multiple scattering calculations of X-ray Absorption Fine Structure (XAFS), X-ray Absorption Near-Edge Structure (XANES) and various other spectra for clusters of atoms. The code yields scattering amplitudes and phases used in many modern XAFS analysis codes, as well as various other properties.

FEFF is a software program used in x-ray absorption spectroscopy. It contains self-consistenr real space multiple-scattering code for simultaneous calculations of x-ray-absorption spectra and electronic structure. Output includes extended x-ray-absorption fine structure, full multiple scattering calculations of varioud x -ray absorption spectraand projected local densities of states. The spectra include x-ray absorption near edge structure, x-ray natural circular dichroism, and non-resonant x-ray emission spectra. Calculations of the x-ray scattering amplitude and spin-dependent calculations of x-ray magnetic circular dichroism and spin-polarized x-ray absorption spectra are also possible, but less automated.

FEFF 9: The newest version is FEFF9 (Version 9.6)

FEFF 9 has a variety of new features and options. First, there are several new spectroscopies that can be calculated with FEFF 9, including electron energy loss spectra (EELS) and non-resonant inelastic x-ray scattering (NRIXS). In addition, there are a variety of improvements. These include; (1) ab initio Debye-Waller factors; (2) improved treatment of inelastic losses; (3) an improved treatment of the core-hole interaction; and (4) more accurate treatment of crystalline systems with the k-space calculation of the Green's function.  FEFF9 comes with the JFEFF GUI.

FEFF 8: 

FEFF 8 improves over previous versions of FEFF by including self consistent calculation of potentials to provide charge transfer and a more accurate estimate of the Fermi level. It also includes full multiple scattering calculations to improve XANES calculations, where multiple scattering expansions can fail to converge. FEFF 8 can output the angular momentum projected density of states, x-ray emission spectra and x-ray scattering amplitudes. The improvements in FEFF 8.40 simplify spin-dependent calculations and can include improved treatment of core-hole and local field effects. FEFF8 now includes JFEFF, a graphical front-end for FEFF 8.4.