Solving the structures of light-atom compounds with powder charge flipping

While the powder charge flipping (pCF) algorithm has been applied successfully to a variety of inorganic compounds, reports on its application to organic structures, in particular those consisting of light atoms only, are rare. To investigate the reason for this apparent incongruity, a series of light-atom structures were tested using the pCF algorithm implemented in the program Superflip. The data sets, which covered varying degrees of reflection overlap, had resolutions of approximately 1 Å, and the structures ranged from 40 to 136 atoms per unit cell. Both centrosymmetric and noncentrosymmetric structures were investigated. A modified pCF approach, which was developed in a separate study, was tested on several compounds whose structures could not be solved by applying the basic pCF algorithm in Superflip. The results show that organic structures with no heavy atoms and low symmetry do indeed test the limits of the pCF algorithm in Superflip. The study has allowed a few guidelines for approaching such problems to be formulated.