STEP– a trial-and-error procedure for crystal structure determination. I. A description of the program system SYSTEM90
STEP– a trial-and-error procedure for crystal structure determination. I. A description of the program system SYSTEM90
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STEP——晶体结构测定的试错程序 I. SYSTEM90 程序系统的描述。
DOI：
10.1107/s0108767394004460
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发表时间：
1994
期刊：
影响因子：
--
通讯作者：
P. Hou
中科院分区：
文献类型：
--
作者：
Y. Hou;M. Gao;L. Li;P. Hou
本文介绍了一种新的试错直接法程序称为STEP。一组强反射，足以解决的结构，分为一个层次的较小的可溶性和连接的子系统。在每个子系统内，反射需要彼此良好连接，假定先前子系统中的所有反射的相位是已知的。一个试错过程，然后提供一个近似解的超定方程组。随后，通过两个可用的切线公式之一来细化相位，然后通过品质因数评估可扩展性。一个新的整体品质因数，XDFOM，已被发现是非常有效的拿起一个正确的解决方案和程序停止时，XDFOM超过4.0。STEP被合并到一个名为STEP 90的软件包中，该软件包已经用四个困难的已知结构和一个困难的未知结构进行了测试。在所有的情况下，一个正确的相位设置被发现。EQUEM90是一个强大的技术，为解决困难和大型结构。
This paper describes a new trial-and-error direct-methods procedure called STEP. A set of strong reflections, sufficient to solve the structure, is divided into a hierarchy of smaller soluble and connected subsystems. Within each subsystem, the reflections are required to be well connected with each other, given that the phases of all reflections in the previous subsystems are known. A trial-and-error procedure is then employed to provide an approximate solution to an overdetermined set of equations. Subsequently, phases are refined by one of two available tangent formulae and then assessed for plausibility by figures of merit. A new overall figure of merit, XDFOM, has been found to be very effective in picking up a correct solution and the procedure is stopped when XDFOM exceeds 4.0. STEP is incorporated in a package called SYSTEM90, which has been tested with four difficult known structures and one difficult unknown structure. In all cases, a correct phase set was found. SYSTEM90 is indicated as a powerful technique for the solution of difficult and large structures.