The Sir2014 flow diagram, shown in below, is a useful guide for understanding the program strategy for ab-initio structure solution.
The MDM approach is particularly efficient for small and medium-sized molecules; the application of the RELAX procedure is a very important tool: it is often able to drive phases with large errors to their correct values. VLD may be used as a valid alternative. SDM is the default phasing approach for electron diffraction data. For proteins the tangent procedures are rather inefficient: a large set of trials have to be explored before finding the useful one. The Patterson deconvolution techniques are frequently able to find the correct solution in few trials, provided some heavy atoms are present in the structure.
In order to reduce CPU times, different strategies have been implemented in Sir2014, depending on the starting phasing approach and structural complexity.
The program stops when a proper fFOM is larger than a given threshold or, for small molecules, the R value is smaller than a threshold.
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