Phase combination and cross validation in iterated density-modification calculations
Phase combination and cross validation in iterated density-modification calculations
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DOI：
10.1107/s090744499500761x
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发表时间：
1996-01-01
期刊：
影响因子：
--
通讯作者：
Main, P
中科院分区：
文献类型：
--
作者：
Cowtan, KD;Main, P
根据已知的化学信息，现在有各种各样的密度修正技术可用于改进电子密度图。然而，这种修改必须始终受到与实验数据一致性的约束。这通常是通过在实际空间中交替进行地图修改周期，并在倒数空间中与实验数据进行重组来实现的。相位重组是基于这样的假设，即密度修正图可以被视为结构的部分模型，其中包含与实验导出的相位无关的信息。这一假设被证明是不正确的，并研究了另一种程序，其副作用是允许计算自由R因子。
A variety of density-modification techniques are now available for improving electron-density maps in accordance with known chemical information. This modification must, however, always be constrained by consistency with the experimental data. This is conventionally achieved by alternating cycles of map modification in real space with recombination with the experimental data in reciprocal space. The phase recombination is based upon the assumption that the density-modified map may be treated as a partial model of the structure which contains information independent of the experimentally derived phases. This assumption is shown to be incorrect, and an alternative procedure is investigated which as a side effect allows calculation of a free R factor.