Crystallography Laboratory University of Nijmegen
CRUNCH
  
- 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:
- If Crunch does not give you the option or
- 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.
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