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• FEFF是一個自洽的多重散射從頭計算XAS譜和電子結構的軟件包。用于X射線吸收精細結構（XAFS），X射線吸收近邊結構（XANES）和原子簇的各種其他光譜的從頭多次散射計算。該代碼產生許多現代XAFS分析代碼中使用的散射振幅和相位，以及各種其他屬性。
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• FEFF 9：新版本是FEFF9（版本9.6）
• FEFF 9具有各種新功能和選項。首先有幾個可以用FEFF 9計算的新的光譜，包括電子能量損失譜（EELS）和非共振非彈性X射線散射（NRIXS）。另外，還有各種改進。這些包括;
• （1）從頭開始的 Debye-Waller因子;
• （2）改善非彈性損失的治療;
• （3）核心 - 空穴相互作用的改進處理;
• （4）用格林函數的k空間計算更精確地處理結晶體系。
• （5）利用基于自洽的球型MT散射勢的實空間Green函數方法, 計算中考慮了polarization dependence, core-hole efects,and local field corrections,et al.
• （6）FEFF9增加了倒空間計算(周期邊界條件)
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• FEFF9附帶JFEFF GUI。
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• FEFF能夠提供如下的計算：
• - 散射振幅: effective scattering amplitude；x-rayelastic scattering amplitude f = f0+f’+if ’’, including Thomson and anomalous parts
• - 相移函數 : ?，effective scattering phase shift
• - 平均自由程 : λ，mean free path
• - 初始路徑長：R0
• - Deybe-Waller因子: σ
• - feffnnnn:
• - chi :
• - …..
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• FEFF9的模塊結構
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• 輸入、輸出處理
• 原子勢計算
• 嵌入的原子勢計算
• 屏蔽效應計算
• ldos計算
• 截面和相移函數計算
• 全多重散射計算
• 求GT的跡
• 路徑計算
• 計算散射振幅和其它XAFS參數
• 計算指定的譜
• 計算多電子激發
• 計算eels
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• FEFF 8：
• FEFF 8 通過包括自我一致的電勢計算來提供電荷轉移和更精確的費米能級估計，改進了FEFF的先前版本。它還包括完全多次散射計算，以改善XANES計算，其中多次散射擴展可能無法收斂。FEFF 8可輸出角動量投影狀態密度，x射線發射光譜和x射線散射振幅。FEFF 8.40的改進簡化了依賴于自旋的計算，并且可以包括對核心孔和局部場效應的改進處理。FEFF8現在包括JEFEFF，FEFF 8.4的圖形前端。
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• 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.
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• 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 which 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 k-space calculation of the Green's function. FEFF9 comes with the JFEFF GUI.
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• 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.