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首页> 外文期刊>Acta Crystallographica, Section B. Structural Science >Retrieval of structure-factor phases in non-centrosymmetric space groups. Model studies using multipole refinements
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Retrieval of structure-factor phases in non-centrosymmetric space groups. Model studies using multipole refinements

机译：非中心对称空间群中结构因子相的检索。使用多极优化的模型研究

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摘要

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.
机译：在非中心对称空间群中为七个不同的分子晶体构造了具有已知量级和相位的结构因子，并使用几种不同的散射因子模型来校准对结构因子相信息的检索。单极模型被证实是不充分的，对相位的估计很差，并且将傅立叶变形电子密度低估了多达50％。除了六亚甲基四胺（HMT）以外，多极模型通常是成功的。结果证实了为HMT设定结构因子幅度的已知难度，但是揭示了在各种非中心对称空间组中相位恢复行为的广谱性，部分取决于具有受限相位的反射次数。对于几种系统（尿素，过氧化氢，L-丙氨酸和硼嗪），结果证实了针对实验数据的散射因子模型的多极细化能够产生高度精确的相，因此具有可靠的电子分布。对于HMT的例外情况，简单的特征值滤波技术能够以与研究的其他非中心对称系统中最好的相当的精度检索相和电子密度。

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