Modulated structures are characterized by a violation of their translation periodicity. Unlike standard structures built of identical unit cells, one or more parameters of modulated structures are slightly changed when moving from cell to cell. These changes can be calculated using special computing methods based on generalized crystallography. Nowadays, almost all modulated structures are calculated by program Jana2006 developed at the Department of Structure Analysis. For details about Jana2006, see http://jana.fzu.cz. A preliminary solution of modulated structures necessary as an input to Jana2006 can be obtained from the program Superflip (http://superflip.fzu.cz), which has been also developed at the department. We are just preparing a new modernised version of Jana2006 called Jana2020.
The crystal structure of a modulated mineral franckeite projected along [100]. Four atomic layers thick pseudotetragonal Q slabs alternate with single-octahedron pseudohexagonal H slabs.
