IUCr journals

Ab initio structure solution by charge flipping. II. Use of weak reflections

Acta Cryst. (2005). A61, 147–152

[Charge flipping algorithms] Success rates for a hard-to-solve structure of the original and new charge flipping algorithms (black and red symbols).
Charge flipping is an amazingly simple iterative algorithm that is based on extended zero regions of the electron density, but not directly on atomicity. In the original version [Oszlányi & Süto (2004). Acta Cryst. A60, 134–141] the phase space was explored by changing the sign of electron density below a threshold δ. This process can be efficiently improved in reciprocal space by handling weak reflections in a special way: their calculated moduli are allowed to change freely and calculated phases are shifted by π/2. Paradoxically, using less observed data as constraints allows the solution of larger structures.

Gábor Oszlányi and András Süto