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Temperature Factor Refinement
In TNT, all parameters of an atom can be varied in the same cycle; having
this ability does not mean that one should use it. The occupancy parameters
cannot be refined without quite high-resolution diffraction data. With
1.6Å data one can refine group occupancies but individual occupancies
are poorly behaved. In most cases, all atomic occupancy fractions in a
model should be fixed equal to one.
Temperature factors present a larger problem. With 1.6Å data one
can refine individual temperature factors without resorting to restraints
that depend on stereochemical relationships among atoms. At the other extreme,
with only 3Å data nothing is gained by refinement of individual temperatures
factors. Handling the ground between is subject to judgement. The decisions
depend on the resolution of the diffraction data and its quality. Table
ii lists my personal criteria for the application of restraints to
the temperature factors of a model.
Dale Edwin Tronrud
Thu Nov 20 13:34:16 PST 1997