CRYSTAL-STRUCTURE DETERMINATION FOR CRYSTALS WITH TWINNING BY HEMIHEDRY OR PSEUDOHEMIHEDRY

An approach to structure determination for a crystal from component crystals in equal volume fractions, the most difficult case to the solution, is outlined with precautions for stepwise initialization. Proper selection of a crystal geometrical symmetry space group from a corresponding twin anti-symmetry space group and interpretation of a Patterson space are indispensable prerequisite for the solution. Observations unique to the case are briefly described in a sequence of Patterson synthesis, Fourier approach and least-squares refinement for efficient interpretation and processing.