Search for a fragment of known geometry by integrated Patterson and direct methods
Search for a fragment of known geometry by integrated Patterson and direct methods
复制标题
通过集成帕特森和直接方法搜索已知几何的片段
DOI：
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发表时间：
1984
期刊：
影响因子：
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通讯作者：
G. Sheldrick
中科院分区：
文献类型：
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作者：
E. Egert;G. Sheldrick
提出了一种方法，试图利用所有的先验可用信息，以定位已知的几何形状的单元格中的片段。而搜索模型的方向是由一个传统的，但高度自动化的真实空间帕特森旋转搜索，它在细胞中的位置是通过最大化的余弦的加权和的一小部分强双折射敏感的三相不变量，从随机位置开始。帕特森最小功能的基础上分子间矢量计算只为那些解决方案，不引起分子间接触短于预设的最小值。这种方法避免了Patterson空间中耗时的细化，对大型结构尤其有效。最后，最佳的解决方案进行排序，根据一个数字的优点的基础上与帕特森功能，三相一致性和R指数涉及Eobs和Ecalc的协议。使用从其他已发表的结构或力场计算中提取的搜索片段，对大约30个已知结构进行的测试表明，Patterson和直接方法的这种新颖组合是可靠的，并且具有广泛的适用性。一些选定的例子表明了计算机程序PATSEE的能力，该程序与SHELX 84兼容，并将与SHELX 84一起分发。PATSEE对所有空间群都是有效和高效的，对原子或数据的数量没有限制。对单个碎片的定向搜索允许一个额外的扭转自由度，并且最多可以同时平移两个碎片。
A method is presented that attempts to exploit all the a priori available information in order to locate a fragment of known geometry in the unit cell. Whereas the orientation of the search model is determined by a conventional but highly automated real-space Patterson rotation search, its position in the cell is found by maximizing the weighted sum of the cosines of a small number of strong translation-sensitive triple-phase invariants, starting from random positions. A Patterson minimum function based on intermolecular vectors is calculated only for those solutions that do not give rise to intermolecular contacts shorter than a preset minimum. This procedure avoids the time-consuming refinement in Patterson space and should be especially efficient for large structures. Finally, the best solutions are sorted according to a figure of merit based upon the agreement with the Patterson function, the triple-phase consistency and an R index involving Eobs and Ecalc. Tests with about 30 known structures, using search fragments taken from other published structures or from force-field calculations, have indicated that this novel combination of Patterson and direct methods is reliable and widely applicable. A few selected examples demonstrate the power of the computer program PATSEE, which is compatible with SHELX84 and will be distributed together with it. PATSEE is valid and efficient for all space groups and imposes no limits on the number of atoms or data. The orientation search for a single fragment allows one additional degree of torsional freedom, and up to two fragments may be translated simultaneously.