测定晶体结构的系统试差法的研究(III) SYSTEM 90程序系统和应用

介绍最近研究的系统试差法的基本公式和它的程序系统ＳＹＳＴＥＭ９０的构成，应用该程序系统对收集到的５个难解结构进行了成功的测定，实验结果显示了ＳＹＳＴＥＭ９０程序系统的威力，最后在分析的基础上，提出了系统试差法程序系统不同于其它直接法的四个特点。

Studies of Trail and Error Method for Cyrstal Structural Determinations(III) Application and Program System of SYSTEM 90

We describe a new trail-and-error direct method procedure called STEP. A set of strong reflections, sufficient to solve the structure, is divided into a hierarchy of smaller soluble and connected sub-systems. After having determinable system, we apply three-phase relationship of system to establish the system phase super solution equations. Then, by means of trail and error method, find out phases satisfying the equations.
A new overall figure of merit t XDFOM, has been found to be very effective in picking up a correct solution and the procedure is stopped whenever XDFOM exceeds 4.0 in value.
The program system of STEP, called SYSTEM 90, has been completed, and tested by four difficult known structures and one difficult unknown structure. Satisfying structure models are shown in the E maps. Finally, we mentioned the four SYSTEM90's features which are different from other direct method program. It has been shown that SYSTEM 90 is very powerful to determine difficult structures.