Section 25.2.1.10.4.2. Multiple-crystal averaging

If multiple crystal forms are available and one has a source of phase information for each crystal form, then averaging over the independent molecular copies within all crystal forms is possible. In fact, one may also have NC symmetry within some of the crystal forms. One can utilize all of this information during averaging by exactly the same process as previously described. For each form, the appropriate envelope mask(s) must be obtained and any internal NC symmetry operators refined, as described earlier. Then operators relating molecules from one crystal form to another must be obtained and refined. The program LSQROTGEN can read in multiple submaps, allowing refinement of the additional operators. The program MAPAVG accepts submaps from up to six different crystal forms. Averaging over all copies then proceeds exactly as described above, except that prior to averaging, density in all submaps is placed on a common scale, and upon completion averaged submap files are written for each crystal form.