Methods for reconstructing `experimental model wavefunctions' from X-ray data are reviewed and clarified, and the key problem of deciding when to terminate the wavefunction reconstruction procedure is defined as 'the halting problem'. The role of Hans-Beat Bürgi in all of this is described.
Advanced simulation methods are used to portray the structural, static and dynamic aspects of the rotations of methyl and trifluoromethyl groups, as well as entire molecules, in their crystals at equilibrium.
Diffuse scattering and inelastic scattering were probed by X-rays and compared for inorganically formed natural calcite and biogenic calcite from the sea urchin spine. The differences in the mechanical properties between the `strong' biogenic and `brittle' abiotic material are attributed to a mesoscopic architecture of the spine.
Reported here is a new metastable phase in flash-frozen disordered Prussian blue analogues characterised by the appearance of diffuse scattering clouds and reduction of the cubic symmetry to a tetragonal or lower space group.
X-ray radiation damage increases unit-cell volume, apparent anisotropic displacement parameters and shifts the spin state equilibrium to lower temperatures. It may therefore serve as another tool to tune a spin transition sequence.
The theory of modulated structures and the study of such materials
constitute an active and healthy field in crystallography. To view visualizations of over 60 modulated stuctures published in Acta Crystallographica Section B, click on the structure below.