Ab initio direct methods: practical advice for getting beyond the first 300 atoms.
Ab initio direct methods: practical advice for getting beyond the first 300 atoms.
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从头开始直接方法：超越前 300 个原子的实用建议。
DOI：
10.1107/s0907444992006231
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发表时间：
1993
期刊：
影响因子：
--
通讯作者：
D. Langs
中科院分区：
文献类型：
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作者：
D. Langs
并不是所有的晶体结构研究都适用于仅用直接方法的相变溶液。指南程序被概述，其目的是帮助评估是否可以期望直接方法程序对大分子结构的衍射数据进行相分析。这一分析针对三个不同的调查层次：(1)原始数据有多好，以及是否可以得出E值来表示点原子结构。(2)通过相位关系进行数据交互的效果如何，以及它们可能会产生稳定的阶段性解决方案。(3)找到可识别的解决方案的预后如何。数据来自对一些大型、难以解决的结构的尸检分析，以说明每一点。应该鼓励直接方法实践者，假设获得解的先验预测是有利的，有足够的计算资源可用，并且施加了足够的持续努力，则有时可以利用现有方法来确定每个不对称单位具有超过300个原子的晶体结构。
Not all crystallographic structural investigations are amenable to a phasing solution by direct methods alone. Guideline procedures are outlined which are intended to help the evaluation of whether direct-methods procedures may be expected to phase diffraction data for large molecular structures. This analysis is directed at three separate levels of inquiry: (1) How good are the primary data and can E values be derived to represent a point-atom structure. (2) How well do the data interact through phase relationships and may they be expected to produce a stable phasing solution. (3) What is the prognosis for finding recognizable solutions. Data are presented from the post-mortem analyses of a number of large, difficult-to-solve, structures to illustrate each of these points. Direct-methods practitioners are to be encouraged that crystal structures having more than 300 atoms per asymmetric unit may occasionally be determined utilizing present methodologies provided that an a priori prognosis for obtaining a solution is favorably high, adequate computational resources are available, and sufficient persistent effort is applied.