摘要
本文从分析R、R_w和e.s.d.表式入手,结合实例讨论了衍射点数对X-射线晶体结构测定结果的影响,提出测定一个晶体结构并能获得较佳结果的最合理衍射点数(NO)至少应该比总变量数(NV)多9～10倍,即NO/NV≥9～10的看法,建议在测定晶体结构工作前期收集衍射数据时,应预估好2θ角范围,保证NO/NV值达到9～10的起码值,以便获得较理想的结构测定结果。
A primary study on the relationship between the numbers of observable reflections (NO) and the final discrepancy R , Rw and estimated standard deviations (e. s. d. ) of parameters is reported in this paper. Based on a briefly theoretical analysis to the formula (e. s. d. ) , a graph of d (the error in an observation of unit weight) as a function of NO/NV was plotted and showed how the rf' s value changed with the change of NO. From the d curve the conclusion of the optimum of the observable reflections NO/NV(?)9-10 (where NV is the number of variations) was led properly to determine and gain a fine crystal structure with minimum discrepancy, accurate parameters and precise e.s.d.'s values, and demonstrated by an example of experimental calculations of single crystal structure.
