Over the past decade, structure determination from powder diffraction data has been widely and successfully used to determine structures of many organic, inorganic and organometallic compounds. Nevertheless, ab initio structure solution from powder data is still a challenge in many cases, due to the inevitable overlap of Bragg reflections resulting from the collapse of the three dimensions of reciprocal space onto the single dimension of a powder diffraction pattern. To develop the full capacity of structure determination from powder diffraction data, new methods, including the direct-methods approach, have to address the correct handling of multiply overlapped reflections.

The dual-space-based Shake-and-Bake procedure is one of the most successful direct methods for phasing single crystal diffraction data. A new method, termed Powder Shake-and-Bake and implemented in the computer program P-SnB, incorporates extracted and overlapped reflections in the Shake-and-Bake procedure. It performs in each SnB cycle (i) an overlapped-reflection partition (via partial structural information from the previous cycle), (ii) a reciprocal-space phase refinement (via the reduction of the values of a statistical minimal function), and (iii) a real-space density modification (via peak picking).

The detailed Powder Shake-and-Bake algorithmic development and implementation, and the successful P-SnB applications with experimental powder diffraction data will be discussed. 

This research was supported by NIH grant GM072023.

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