Use of the tangent formula for the refinement of neutron protein data.

The tangent refinement technique has been shown to work marginally for protein neutron data, at least to the extent that the images of all atoms except hydrogen are sharpened. However, the process is very sensitive to over-refinement, and all the maps were sharpened excessively. Refinements in the squared structure were more stable, and the maps were somewhat better than those from the original structure refinement. This technique might be helpful in certain instances, but the poor quality of the maps prevents it from being generally useful. Perhaps the tangent refinement technique will be more fruitful in application to neutron protein data when experimental phase information is available.