This is an archive copy of the IUCr web site dating from 2008. For current content please visit https://www.iucr.org.

Next: 4. Examples Up: Crystal Structure Analysis Using the `Superposition' Previous: 2.2 The Application of Direct Methods Atoms

3. Steps of Structure Determination

1. Determine the space group and unit cell of the real structure.

2. Test for systematically strong intensities.

3. Determine the space group of the superposition structure (see examples).

4. Determine the superposition structure ${\rho}_{\mbox{sup}}(x, y, z)$ or at least the heavy atom positions(s) in ${\rho}_{\mbox{sup}}(x, y, z)$ .

5. Determine the complementary structure ${\rho}_{\mbox{com}}(x, y, z)$ or the real structure.

5.1 Compute and discuss the Patterson function of the complementary structure, if this corresponds to the systematically weak reflection.

5.2 Apply `Direct methods' (see above).

5.3 Apply the method of `linear structure factor equations'.

5.4 Resolve the ambiguity of the superposition structure using chemical knowledge, such as minimum distance between atoms, knowledge of groups, coordination polyhedra etc.

IUCr Webmaster