Flack H D, Sadki M, Thompson A L, Watkin D J
Département de Chimie Minérale, Analytique et Appliquée, University of Geneva, Switzerland.
Acta Crystallogr A. 2011 Jan;67(Pt 1):21-34. doi: 10.1107/S010876731004287X. Epub 2010 Dec 7.
The practical use of the average and difference intensities of Friedel opposites at different stages of structure analysis has been investigated. It is shown how these values may be properly and practically used at the stage of space-group determination. At the stage of least-squares refinement, it is shown that increasing the weight of the difference intensities does not improve their fit to the model. The correct form of the coefficients for a difference electron-density calculation is given. In the process of structure validation, it is further shown that plots of the observed and model difference intensities provide an objective method to evaluate the fit of the data to the model and to reveal insufficiencies in the intensity measurements. As a further tool for the validation of structure determinations, the use of the Patterson functions of the average and difference intensities has been investigated and their clear advantage demonstrated.
研究了在结构分析的不同阶段弗里德尔对映体平均强度和差值强度的实际应用。展示了这些值在空间群确定阶段如何合理且实际地使用。在最小二乘精修阶段，结果表明增加差值强度的权重并不能改善它们与模型的拟合度。给出了差值电子密度计算系数的正确形式。在结构验证过程中，进一步表明观察到的和模型差值强度的图提供了一种客观方法，用于评估数据与模型的拟合度并揭示强度测量中的不足。作为结构确定验证的另一种工具，研究了平均强度和差值强度的帕特森函数的使用，并证明了它们的明显优势。
