Structure Solution – Inorganics
Learning outcomes: Topas has lots of different methodologies built in for solving inorganic structures using simulated annealing. The approach used is to combine random movements of atoms/groups with rapid refinement of diffraction data. One can anneal coordinates of individual atoms or groups of atoms expressed as rigid bodies or using z-matrices. One can refine against powder or single crystal data. Powder data can be expressed as “pseudo single crystal data” by just considering peak intenisities in a number of ways. One can also use charge flipping methodologies which won’t be covered in this course.
Methodology: Structure solution is outside the remit of this course, though covered in several tutorials. Some of the suggestions below are based on Alan’s built in examples.
1. Try running pbso4_solve.inp. This uses simulated annealing on powder data expressed in a “short cut” way to solve the structure of PbSO4. It’s derived from some of Alan’s data.
2. Go to the main Topas menus and find the Examples subfolder. In “Charge-Flipping Powder” try running cf-alvo4-pawely.inp then cf-alvo4.inp which solves the structure of AlVO4 using charge flipping.
3. In “Charge-Flipping Single Crystal” try running cf-pn02.inp. This solves the structure of a 441 atom molybdenum phosphate using charge flipping.
4. If you’re feeling brave try looking on line for datasets from pervious structure solution challenges.