Accurate structure analysis by the maximum‐entropy method
Accurate structure analysis by the maximum‐entropy method
复制标题
DOI：
10.1107/s0108767389012377
复制
发表时间：
1990-04
期刊：
影响因子：
--
通讯作者：
M. Sakata;Masumi Sato
中科院分区：
文献类型：
--
作者：
M. Sakata;Masumi Sato
Si晶体的电子密度图由最大熵方法（MEM）绘制，其中30个结构因子由Pendellosung方法在绝对尺度上非常精确地确定[Saka & Kato（1986）. Acta Cryst.A42，469-478]。它示出了以下三个有益的点出现从使用的MEM精确的结构分析。首先，可以获得精确的电子密度图;在最大熵图中，成键电子的存在是清晰可见的，即使在分析中不包括禁止反射。由222和442个禁戒反射的最大熵图计算的结构因子与不同实验测量的结构因子吻合较好。最终的R因子为0.05%，这是由于测量的结构因子的高精度。其次，不需要寻求一个更好的结构模型，这可能是一个复杂和耗时的过程，在准确的结构分析。第三，最大熵图的分辨率远高于传统傅里叶变换图。还发现，在硅的情况下，相位信息不是绝对必要的，因为可以在没有任何相位信息的情况下获得与利用所有相位信息绘制的图完全相同的密度分布图。
The electron-density map of an Si crystal is drawn by the maximum-entropy method (MEM) with 30 structure factors which were determined very accurately on an absolute scale by the Pendellosung method [Saka & Kato (1986). Acta Cryst. A42, 469-478]. It is shown that the following three beneficial points arise from the use of the MEM for accurate structure analysis. Firstly, a precise electron-density map can be obtained; the existence of bonding electrons is clearly visible in the maximum-entropy map, even though no forbidden reflections are included in the analysis. The structure factors calculated from the maximum-entropy map for the 222 and the 442 forbidden reflections show good agreement with those measured by different experiments. The final R factor was 0.05% as a consequence of the high accuracy of the measured structure factors. Secondly, there is no need to seek a better structural model which could be a complicated and time-consuming process in accurate structure analysis. Thirdly, the resolution of the maximum-entropy map is much higher than that of the map drawn by conventional Fourier transformation. It is also found in the case of silicon that phase information is not absolutely necessary because exactly the same density-distribution map can be obtained without any phase information as the map drawn with all the phase information.