求解非中心对称晶体结构的人工相位退化法

在用直接法推引非中心对称晶体结构因子的相位时,如果人为地使相位退化为实分量的正负号,可以获得同时包含真实结构及其对映体的E图。利用分量关系式不难使这样的E图复原,从而解出结构。这样做,对于每一个参加相位排列的起始衍射只需考虑两种可能的相位值(0或π),因而比通常的相位排列法节省计算量。关键词：

ARTIFICIAL PHASE DEGENERATION IN THE DETERMINATION OF NON-CENTROSYMMETRIC STRUCTURES

During the phase derivation in the case of non-centrosymmetric crystal structure, if one forces the phases to degenerate into a set of signs corresponding to those of the real parts of structure factors, it then results in an E-map containing simultaneously the actual structure and its enantiomorph. Such an E-map may in turn easily be retrieved by use of the component relation leading to a unique solution of the structure. With this procedure only two possible values (0 or π) are necessary to be considered for each unknown phase within the starting set. Hence the amount of calculation can be greatly reduced as compared with that of the ordinary phase permutation method.