NEW METHODS IN XAFS DATA ANALYSIS: X RAY

扩展X射线吸收精细结构EXAFS Debye-Waller 因子是EXAFS理论中的一个重要术语， 解释了样品的结构和热无序。 必须知道单次和多次散射的德拜-沃勒因子 准确地获得理论和 实验 由于可以被 通过拟合实验数据确定的是有限的，一般来说，数据 不能支持所有相关多重散射的拟合 Debye-Waller因子 我们已经发展出计算能力 这些从头算多重散射DWFs直接从已知的或 假想的三维结构。 这是必要的第一步 迈向多重散射拟合实用方法的一步， 不使用fudge-factor。 在我们的第一篇论文（发表在Phys. Rev. B.）我们调查了各种计算的充分性， 小尺度振动结构的计算方法 分子。 分析表达式推导出多个 基于平面波的散射Debye-Waller因子 近似，这似乎是足够的，为这一目的。 两 半经验哈密顿（ZINDO）和从头算密度 用函数程序（DGAUSS）计算了简正模 特征频率和特征向量。 使用内部编写的程序， 这些数据被用来计算所有的单散射和多散射 Debye-Waller因子最多可达四个原子团簇。 从头算 Debye-Waller因子与根据以下公式计算的因子进行了比较： 实验红外和拉曼频率。 良好的一致性 在所有情况下都观察到，为可行性提供了强有力的支持， 计算精确的多重散射德拜沃勒因子 蛋白质中的氨基酸残基。

The extended x-ray-absorption fine structure EXAFS Debye-Waller factor is an essential term appearing in EXAFS theory, and that accounts for the structural and thermal disorder of a sample. Single-and multiple-scattering Debye-Waller factors must be known accurately to obtain quantitative agreement between theory and experiment. Since the total number of parameters that can be determined by fitting experimental data is limited, in general, data cannot support fitting of all relevant multiple-scattering Debye-Waller factors. We have developed the ability to calculate these ab initio multiple scattering DWFs directly from the known or hypothetical three-dimensional structure. This is a necessary first step toward a practical approach to multiple scattering fitting, without use of fudge-factors. In our first paper (published in Phys. Rev. B.) we investigated the adequacy of various computational approaches for calculating vibrational structure within small molecules. Analytical expressions were derived for multiple scattering Debye-Waller factors, based on the plane wave approximation, which appears to be adequate for this purpose. Both semiempirical Hamiltonians (ZINDO) and the ab initio density functional programs (DGAUSS) were used to calculate the normal mode eigenfrequencies and eigenvectors. Using programs written in-house, these data were used to calculate all single- and multiple-scattering Debye-Waller factors up to a four atom cluster. The ab initio Debye-Waller factors were compared to those calculated from experimental infrared and Raman frequencies. Good agreement was observed for all cases, lending strong support for the feasibility of calculating accurate multiple scattering debye waller factors for amino acid residues in proteins.