Ab initio determination of incommensurately modulated structures by charge flipping in superspace
The
ab initio structure solution algorithm dubbed 'charge flipping' [Oszlányi & Süto (2004).
Acta Cryst. A
60, 134–141] has been generalized towards (3+
d)-dimensional superspace. This generalized algorithm allows for the solution of incommensurately modulated structures directly in superspace. This eliminates the necessity of solving the basic structure of the modulated compound, which can be an extremely difficult task in the case of complex modulations. The algorithm succeeded in solving seven of eight tested incommensurately modulated structures. The method has been demonstrated on the modulated structure of tetraphenylphosphonium hexabromotellurate(IV) bis{dibromoselenate(I)}.
Lukáš Palatinus
![[modulation function]](https://www.iucr.org/__data/assets/image/0005/18950/12-4_Page_08_Image_0005.jpg)
The x, y, and z components (circles, squares, and triangles, respectively) of the modulation function of a Br atom as obtained from the charge flipping algorithm (red symbols) and from the final structure model (green symbols).
