RESUMEN
The crystal studied is a 0.545 (1):0.455 twin, space group C\bar 1, Z = 16, and is a commensurate occupational and displacive modulation of a Z = 4 idealized parent structure with the space group A2/a and a(p) = a/2, b(p) = b/2, c(p) = c. A hierarchical approach to solution and refinement led sequentially to structures in the space groups A2/a, P2(1)/n, P\bar 1 and finally C\bar 1. The major and minor components of the reflection intensities could be identified using irreducible representations of A2/a and P2(1)/n, which in turn suggested suitable constraints and restraints for optimizing the refinement pathway. Comparative refinement was used to show the correctness of the final structure solution and how appropriately chosen constrained refinement allowed an escape from a false minima.