[ccp4bb]: Geometry problems in Refmac

["Ben Sandler" <sandler@msg.ucsf.edu>]

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It appears now that my ligand geometry problems arise from 
two sources:

* I'm refining a low (3.1A) resolution structure, and I 
didn't have the matrix weight low enough.  Now that I've 
set it to 0.1, things are looking much better.  Is this 
roughly the weight I should be expecting to use for 3.1A?

* Even with the weight set to 0.1, I'm still having 
problems with a hydroxyl group in the ligand.  The 
hydroxyl is sandwiched between two iodines, and there's no 
electron density for it.  (I'm assuming that this is the 
result of series termination errors stemming from the two 
iodines having such dense electron density.)  As a result, 
the hydroxyl is strongly pulled into the electron density 
of one of the iodines, causing a consistent bend of about 
10 degrees.  Is there any good way to prevent this from 
happening?  The most obvious seems to be to set the 
occupancy of the hydroxyl very low until the very last 
cycle of refinement, but that doesn't feel entirely kosher 
to me.

-Ben Sandler