Phasing via SAD/MAD data:: the method of the joint probability distribution functions
Phasing via SAD/MAD data:: the method of the joint probability distribution functions
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DOI：
10.1107/s0907444903022406
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发表时间：
2004-01-01
期刊：
影响因子：
--
通讯作者：
Siliqi, D
中科院分区：
文献类型：
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作者：
Giacovazzo, C;Siliqi, D
应用联合概率分布函数的方法，在预先定义了反常散射子结构的条件下，导出了MAD情况下能精确定相反射的概率公式。数学方法考虑了测量和模型误差，它们被视为原始随机变量，以及定义晶体结构未知部分的原子位置。概率公式具有经典的正切表达式。所有影响相位估计的参数都可以直接用实验量来解释：e.异常和色散差异，误差的大小和归一化结构因子模量。该公式已被应用于几个实际情况：一个程序也被设计，这是能够细化的阶段，并导致易于解释的电子密度图。
The method of the joint probability distribution functions is applied to derive a probabilistic formula which is able to phase reflections in the MAD case accurately, under the condition that the anomalous- scatterer substructure has been defined previously. The mathematical approach takes into account both measurement and model errors, which are treated as primitive random variables, as well as the atomic positions defining the unknown part of the crystal structure. The probabilistic formula has the classical tangent expression. All the parameters influencing the phase estimation are immediately interpretable in terms of experimental quantities: i. e. anomalous and dispersive differences, magnitude of the errors and normalized structure- factor moduli. The formula has been applied to several practical cases: a procedure has also been designed which is able to refine the phases and lead to easily interpretable electron- density maps.