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小木虫论坛-学术科研互动平台 » 材料区 » 晶体 » 晶体解析 » 怎么看自己单晶数据的好坏，解析之后 多谢
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1chenqiliang

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[交流] 怎么看自己单晶数据的好坏，解析之后 多谢

多谢了
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1楼 2016-05-21 11:23:30
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1chenqiliang

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R-factor  是什么意思
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无论生活怎样，静心面对。
2楼2016-05-21 21:15:00
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liudanna
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1chenqiliang: 金币+1, 多谢 2016-05-24 19:29:59
R值

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3楼2016-05-23 13:12:43
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1chenqiliang

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3楼: Originally posted by liudanna at 2016-05-23 13:12:43
R值

r多大为好   还有就是论文对  单晶数据的要求
详细点好   谢谢
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4楼2016-05-24 19:29:37
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etongtong

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小木虫: 金币+0.5, 给个红包，谢谢回帖
1chenqiliang: 金币+2, 谢谢 2016-05-25 23:18:13
大致上有那么几条：
1 收敛，不收敛表明没有解析完毕，在CIF的_refine_ls_shift/su_max           0.001中这个数值一般要小于0.01
2 鬼峰，如果没有重原子的话，Q峰的峰值要小于1；如果有重原子，大于1的Q峰要出现在重原子附近才合理。有人问为啥有这种情况，比如你有未解析出来的溶剂小分子，这个时候常常出现鬼峰
3 就是大家都熟悉的R值，还有Goof,这些就不赘述了
4 数据的完整度常常被大家忽略，它出现在CIF文件的最后了_diffrn_measured_fraction_theta_max    0.967 这个不小于0.96；_diffrn_reflns_theta_full              25.05 这个值一般不小于50
先说这么多哇，我以前总结过一个，后来丢失了。欢迎方家补充
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5楼2016-05-25 18:08:53
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etongtong

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小木虫: 金币+0.5, 给个红包，谢谢回帖
你金币这么少，还给我，不必了，我给你个标准答案吧:
Structure Refinement Checklist

Completed crystal structures must pass the following tests.

1.The bonds in the model must be chemically reasonable. Similar bonds should have similar geometries, and all bond lengths, angles, etc., must match literature values.


2.There should be no atoms with displacement parameters that are non-positive definite, npd. The displacement parameters should be checked for signs of systematic error. For example, ellipsoids of several heavy atoms aligned in one direction may indicate the need for a better absorption correction. Nonspherical or large ellipsoids suggests that the model may need to include disorder.


3.The structure should be refined to convergence, that is the maximum shift/error ratio should be < 0.05. All non-hydrogen atoms should be refined with anisotropic displacement parameters provided that there are at least 10 data per parameter. Lower data-to-parameter ratios indicate that either the data were not collected to a high enough scattering angle, or that Friedel-related (or equivalent) data were not collected for a structure in a noncentrosymmetric space group.


4.Noncentrosymmetric space groups should be refined with the correct absolute structure. If anomalous scattering is being used to determine the absolute configuration, then the sample must contain atoms with sufficient differences in anomalous scattering to yield a meaningful absolute structure result. For example, the absolute structure cannot be determined under either of the following conditions, only one type of atom (besides hydrogen) and any type of radiation, or only first row atoms while using Mo Kα radiation. Also the data must be collected with sufficient quality (sufficient count times) to produce large (>10) mean F2/σ. The best test for absolute structure is the Flack test.6


5.The weighting scheme should be adjusted so as to produce nearly constant values for the variances as functions of intensity and resolution. Doing this will also make the goodness of fit, S, have a value around 1.0.


6.There should be no peaks with strong intensities in a list of “worst-fitting data.”


7.The final difference map should have no abnormally high peaks or low valleys.


8.The final R1 and wR2 should be reasonably low for the quality of data. Good small molecule crystal structures usually have R1 < 0.05. Acceptable small molecule crystal structures typically have R1 < 0.10.


References
1.G. M. Sheldrick, SHELXTL Reference Manual, 1997, Bruker-AXS, Inc., Madison, WI
2.A. J. C. Wilson, Acta Cryst., 1976, A32, 994-996.
3.H. D. Flack & D. Schwarzenbach, 1988 Acta Cryst., 1988, A44 499-506.
4.W. C. Hamilton, Acta Cryst., 1965, 18, 502-510.
5.D. Rogers, Acta Cryst., 1981, A37, 734-741.
6.H. D. Flack, Acta Cryst., 1983, A39 876-881.
7.R. W. W. Hooft, L. H. Straver, and A. L. Spek, J. Appl. Cryst., 2008, 41, 96-103.
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6楼2016-05-25 23:27:19
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1chenqiliang

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6楼: Originally posted by etongtong at 2016-05-25 23:27:19
你金币这么少，还给我，不必了，我给你个标准答案吧:
Structure Refinement Checklist

Completed crystal structures must pass the following tests.

1.The bonds in the model must be chemically reas ...

谢谢  ，，，，，，，，，，，
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无论生活怎样，静心面对。
7楼2016-05-28 12:38:20
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