Crystallography Laboratory University of Nijmegen

Sometimes heavy atoms are disordered, for instance the chlorine in a perchlorate may be quite "mobile". If you expect something like that treat your structure as an equal atom one. Sometimes changing the cell contents - in 'code.crysin' - is needed in order to do this:
1. If Crunch does not give you the option or
2. You have a largish organic molecule containing one or two sulfur or chlorine atoms. If Crunch has problems finding a solution, even if you told the system it is dealing with an equal atom problem, change the cell contents in your 'code.crysin' file, replacing the heavy atoms by an equivalent number of oxygen atoms.
Atoms such as P, S and Cl are heavy in the context of Crunch. That is compared to first row elements such as C and O etc.
If you have a transition metal or any even heavier element in your compound DO NOT specify Cl and the like as heavy atoms.
If something has gone wrong, e.g. you've started Crunch while you didn't mean to and next interrupted the proceedings by 'Control c', ALWAYS start again by using the Crunch option 'clear': Type
```
crunch code clear
```
This will clean up your directory, preventing otherwise inexplicable failures.