起始相位的受限排列

在含重原子晶体结构的测定中,重原子贡献的相位是一个非常重要的信息。利用重原子相位作电子密度逼近或者Karle迭代是求解含重原子晶体结构的重要手段。但是,当重原子的贡献不占主导地位,或者当重原子分布的对称性高于整个结构的对称性时,上述方法就不易奏效。这时的重原子信息是否还可以用来大大简化结构分析的过程?这是一个值得探讨的问题。本文提出利用重原子的相位来限制直接法中起始相位的排列方式。这样可以成倍地缩减起始相位排列的种数。这一方法同作者提出的另一方法相配合可以使直接法在测定含重原子晶体结构方面的效能大为提高。 关键词：

RESTRAINED PERMUTATION OF THE STARTING PHASES

The heavy atom phases are extremely important in solving crystal structures containing heavy atoms. Successive Fourier approximation and Karle recycling procedures starting with the heavy atom phases are two major methods of solving structures containing heavy atoms. However, difficulties may some times happen when the contribution of heavy atoms is too small to dominate sufficient number of phases or if the distribution of heavy atoms possesses a higher symmetry than that of the whole structure. It is worthy to investigate in these cases whether or not the heavy atom information can still be used to simplify the process of structure determination greatly. In this paper a method is proposed that the heavy atom phases may be used to restrict the permutation of the starting phases leading to a great reduction in number of the starting phase seta. This method incorporating with that proposed by the authors can improve greatly the efficiency of direct methods in solving structures containing heavy atoms.