Section 14.2.2.8. Generation of model X-ray data sets

An important feature of Solve is the inclusion of modules for the generation of model data. Solve can construct model raw X-ray data for either MIR or MAD cases. The macromolecular structure can be defined by a file in PDB format (Bernstein et al., 1977) with heavy-atom parameters defined by the user. Any degree of `experimental' uncertainty in measurement of intensities can be included, and limited non-isomorphism for MIR data in which cell dimensions differ for native and any of the derivative data sets (but in which the macromolecular structure is identical) can be included. This automatic generation of model data is very useful in evaluating what can and what cannot be solved. Once a data set has been generated, the Solve algorithm can be used to attempt to solve it. Solve generates a model electron-density map based on the input coordinates, and during the structure-solution process all maps calculated with trial solutions can be compared to the model map. In many cases, heavy-atom solutions can be related to different origins (and to different handedness as well). The origin shift is identified by Solve by finding the shift that best maps the trial solution onto the (known) correct solution.