Ab initio phasing of X-ray powder diffraction patterns by charge flipping

A fast and effective ab initio algorithm for determining charge-flipping phases directly from indexed powder diffraction patterns has been developed. An indexed powder X-ray diffraction pattern is in principle equivalent to angle-integrated diffraction data, acquired from a single crystal. The algorithm solves degeneracy problem by applying spherical averaging for overlapping Bragg reflection. Relative intensity ratio of degenerate components were calculated by Fourier transform of the current density estimate in each iteration. The process of peak decomposition and phasing were integrated within the same iteration, and a dynamic support is also used. The algorithm provides a powerful new method for initial phasing of diffraction data. Experimetal results show that the algorithm as a robust tool for the phasing of powder diffraction data, intended for phase identification, and can be applied for more complicated structures such as protein crystal structures.