Retrieval of Structure‐Factor Phases in Non‐centrosymmetric Space Groups. Model Studies Using Multipole Refinements
Retrieval of Structure‐Factor Phases in Non‐centrosymmetric Space Groups. Model Studies Using Multipole Refinements
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使用多极细化检索非中心对称空间群模型研究中的结构因子相。
DOI：
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
P. G. Byrom
中科院分区：
文献类型：
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作者：
M. Spackman;P. G. Byrom
已知的幅度和相位的结构因子构造为七个不同的分子晶体在非中心对称空间群，并用于校准检索的结构因子的相位信息与几个不同的散射因子模型。单极模型被证实是不够的，产生差的相位估计和低估的傅立叶变形电子密度高达50%。多极模型通常是成功的，但六亚甲基四胺（HMT）是一个明显的例外。结果证实了已知的困难的HMT的相位结构因子的幅度，但揭示了广泛的频谱的行为的相位检索在各种非中心对称的空间群，部分取决于限制相位的反射的数量。对于几个系统（尿素，过氧化氢，L-丙氨酸和环硼氮烷）的结果证实，多极细化的散射因子模型对实验数据能够产生高度准确的相位，因此可靠的电子分布。对于HMT的例外情况下，一个简单的本征值滤波技术，使检索的相位和电子密度的准确性相媲美的最好的其他非中心对称系统的研究。
Structure factors with known magnitude and phase are constructed for seven different molecular crystals in non-centrosymmetric space groups and used to calibrate the retrieval of structure-factor phase information with several different scattering factor models. Monopole models are confirmed to be inadequate, yielding poor estimates of phases and underestimating the Fourier deformation electron density by as much as 50%. Multipole models are generally successful, with the conspicuous exception of hexamethylenetetramine (HMT). The results confirm the known difficulty of phasing structure-factor magnitudes for HMT, but reveal a broad spectrum of behaviour of phase retrieval in various non-centrosymmetric space groups, depending partly on the number of reflections with restricted phases. For several systems (urea, hydrogen peroxide, l-alanine and borazine) the results confirm that multipole refinements of scattering factor models against experimental data are capable of yielding highly accurate phases and hence reliable electron distributions. For the exceptional case of HMT a simple eigenvalue filtering technique enables retrieval of phases and electron densities with an accuracy comparable to the best of the other non-centrosymmetric systems studied.