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The DEMON/ANGEL suite of computer programs has been developed to carry out density modification by non-crystallographic symmetry-averaging, solvent-flattening and histogram-mapping techniques. This suite consists of programs that allow molecular envelopes to be defined and modified, non-crystallographic symmetry operators to be refined either within one crystal form or between several crystal forms, and iterative density modification to be carried out, including non-crystallographic symmetry averaging of electron densities within or between crystal forms.
Vellieux et al. (Thu,) studied this question.