[ccp4bb]: I to F... and F^2 refinement

[bds <bds@uic.edu>]

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F^2 refinement is generally standard in small molecule refinement, and now 
becoming more accepted with the use of SHELX.  The main difficulty with 
protein refinement with F^2 is (1) determining a reasonable overall scale 
factor, since the model is poor, and (2) using initially unit weights, rather 
than 'real' weights.  The general approach now in use is to refine the protein 
structure to the best model with CNS, etc., and then use SHELX.  If there are 
problems, you will notice that the B's are chaotic.

Bernie Santarsiero