如何用一般反射规定原点和选择对映体

原点规定除P1空间群外,所有非中心对称空间群都有特殊和一般两种反射。习惯上总是用或尽可能用特殊反射的位相给值规定允许原点。而目前的直接法都是用已知位相的线性组合个别推导位相。所以作为起始套组成部分的原点定义反射应该是|E|值大而且参与线性组合次数

How to Specify Origin and Enantiamorph with General Reflections

For non-centrosymmetric crystal structures, it is usually uses as many specila refletions as possible to define origin and enantiamorph. But in some cases, special reflections may be not enough or may be not in good quality to specify origin and enantiamorph so questions about specifying origin and enantiamorph with general reflections are discussed in this paper. Origin definition reflections of any space groups are differentiated into absolute freedoms and relative freedoms so that the problem of assigning values to the general refection phases for specifying origin is able to be solved. The concept of freedom is also used in enantiamorph specification. Two cases about enantiamorph specification relection related to or not related to origin definition refections are disecussed respectively. In both cases enantiamorph specification can be realized through two steps: (1) Chosing the signs of a certain number of structurral invariants (2) On the basis of step one, making restrictins to the amplitudes and phase signs of the invariant's component reflections.