Some different strategies of least-squares refinement of a molecule.
Refinements of a macromolecule (ribonuclease-A) based on structure amplitudes, magnitude of F, and structure amplitude squares, magnitude of F2, were carried out and the results compared. Although the conventional R values are higher for the magnitude of F2 refinement, positional parameters from both types of refinement were not significantly different. However, the mean-square displacements from magnitude of F2 refinements were systematically higher than for those using magnitude F. Various resolution windows and weighting schemes were employed during the work. Electron density maps were examined for magnitude of F2 refinements and were very similar to those using magnitude of F in spite of a conventional R factor of 0.29 using all 1.4 A data. While magnitude of F2 refinements may be formally more correct than magnitude of F refinements, there is little evidence that magnitude of F2 refinement is superior provided that a reasonable weighting strategy is adopted.
Harris
G W
GW
Department of Crystallography, Birkbeck College, London, England.
Moss
D S
DS
D016018:Least-Squares Analysis; D012259:Ribonuclease, Pancreatic / Q000737:chemistry*; D014961:X-Ray Diffraction
D012259:Ribonuclease, Pancreatic