Use of the Consistency Check in the Vector Verification Method

The consistency check is a type of frequency check in which full use is made of the space group symmetry. It is designed for application to a symmetry map, to a tentative atom map, to the results of superpositions, or to any pseudoelectron-density map. Like the frequency check, its purpose is to aid in the analysis of one of the above maps by assigning a relative weight (relative weight equals the number of other peaks that the given peak is consistent with) to the peaks in these maps. To determine the relative weight, each peak in the map is compared with each of the others to see if it is consistent. Two peaks are considered consistent with each other, if and only if, the set of unique vectors between the two is present in the Patterson map. The method is equivalent to doing a full set of symmetry superpositions at each peak in a symmetry map or a tentative atom map; counting the number of points in the resulting map; and outputting this number at the initial peak position. No assumptions other than that for space group symmetry are required to apply the consistency check to a symmetry map. The resulting map, which has been calculated in a routine fashion directly from the Patterson map, may then be conveniently used as the starting point for the structure analysis of an unknown compound.