Question

Exercise Let us consider the monoclinic space group denoted by P2e, whose coordinates of the equivalent general positions are: 4/X; 1/2-Y: 1/2+Z Find the extinction condition.

Answer 1

Solution: For monoclinic space group:

The general coordinates for the given space group will be: $-X;\frac{1}{2}+Y; \frac{1}{2}-Z$

As:

The $2_{1}$ axis of the group symbol repeats the point x, y, z at $-x, +y, z+^{\frac{1}{2}}.$ The c glide (perpendicular to b) repeats x, y, z at $-x, -y^{\frac{1}{2}},z$ and the point $-x, +y, z+^{\frac{1}{2}}.$ at $-x, ^\frac{1}{2}+y, ^\frac{1}{2}-z,$ hence four different position are obtained.