Parallel solutions to the phase problem in X-ray crystallography: An update

The central problem of single crystal molecular structure determination via x-ray diffraction is the "phase problem."Associated with each diffraction maximum are a magnitude, which can be experimentally determined, and a phase angle, which is lost in the experiment. The goal of "direct methods" is to mathematically reconstruct the phase information from the magnitude information alone. The traditional approach of direct methods is capable of determining structures of moderate complexity. The extension of this approach to problems of the size of macromolecules is hampered by the inherent limitations of the traditional approach. Recently, a new formulation of the "phase problem," dependent on a minimal function, has been proposed. This requires the determination of a set of phases which minimize the function. This work is a continuation of [1]. In this paper, we present the Shake-and-Bake method of structure determination. This is a new process aimed at determining structures via minimization and repeated Fourier transformations between reciprocal and real space. Implementation details on a network of Sun4 workstations will be given. In addition results will given for structures of sizes 28 and 84 atoms.