An efficient molecular-replacement translation function based on the evaluation of direct-methods phase invariants.
An efficient molecular-replacement translation function based on the evaluation of direct-methods phase invariants.
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基于直接方法相不变量评估的有效分子替换翻译函数。
DOI：
10.1107/s0108767391009789
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发表时间：
1992
期刊：
影响因子：
--
通讯作者：
Langs,DA
中科院分区：
文献类型：
--
作者：
Langs,DA
传统的分子置换平移函数是基于观察到的衍射振幅和计算出的振幅和相位的搜索片段作为位移矢量的函数的相关分子变换的直接或倒数空间相关性。已经描述的替代方法是基于评估作为搜索模型在单位单元中的位置的函数的相位不变量的列表，并且寻找满足如由概率论预测的这些不变量的期望值的那些区域。如最初制定的，该过程需要迭代计算相位和评估不变量列表，因为搜索模型在定义单位单元的不对称部分的网格点上步进。描述了一种新的计算过程，其中不变量的值仅表示为位移矢量r的函数，作为傅立叶级数，其可以通过标准快速傅立叶变换（FFT）来评估，而不必基于每个网格点处的搜索模型来计算和插入相位的值。
Traditional molecular-replacement translation functions are based on direct- or reciprocal-space correlations between the observed diffraction amplitudes and the calculated amplitudes and phases of the symmetry-related molecular transforms of the search fragment as a function of the displacement vector. An alternative method that has been described is based on evaluating a list of phase invariants as a function of the position of the search model in the unit cell and seeking those regions which satisfy the expectation value of these invariants as predicted by probability theory. As originally formulated, this procedure required the iterative computation of the phases and the evaluation of the list of invariants as the search model was stepped over the grid points defining the asymmetric portion of the unit cell. A new computational procedure is described whereby the values of the invariants are expressed solely as a function of the displacement vector r as a Fourier series that can be evaluated by a standard fast Fourier transform (FFT) without having to compute and insert the values of the phases based on the search model at each grid point.