Aperiodic order coming of age: from inorganic materials to dynamic protein superstructures

A collection of articles from presentations at the Aperiodic 2018 conference is introduced.

CO₂ adsorption in Y zeolite: a structural and dynamic view by a novel principal-component-analysis-assisted in situ single-crystal X-ray diffraction experiment

In situ single-crystal X-ray diffraction data were used to unravel the structural dynamics and enthalpy and entropy of adsorption of CO₂ into Y zeolite. A principal-component-analysis- (PCA) based approach is applied in an innovative way to single-crystal X-ray diffraction data analysis, allowing one to selectively detect the information from the subset of active atoms. The potential of and limitations of PCA in single-crystal diffraction are discussed.

High-speed tensor tomography: iterative reconstruction tensor tomography (IRTT) algorithm

A fast and robust reconstruction algorithm for small-angle scattering tensor tomography, named iterative reconstruction tensor tomography, is presented. It employs a second-rank tensor model and an iterative error backpropagation to simplify and accelerate tensor tomography reconstruction.

Shape transform phasing of edgy nanocrystals

Reconstruction of an object from the averaged coherent diffracted intensity of finite crystals of that object with arbitrary lattice occupancies is possible. An algorithm capable of reconstructing both the so-called averaged shape transform and the object density at the same time is demonstrated.

Characterizing modulated structures with first-principles calculations: a unified superspace scheme of ordering in mullite

Quantitative parameters of modulated crystal structures are determined from density functional theory calculations applied to superstructures obtained using the superspace formalism. The example of mullite is used to demonstrate that with this approach versatile aspects ranging from ordering phenomena to phase diagrams can be understood on a new level.

Ted Janssen and aperiodic crystals

Ted Janssen's contributions to the field of aperiodic crystals are reviewed.

A side-by-side comparison of the solidification dynamics of quasicrystalline and approximant phases in the Al–Co–Ni system

The nucleation and growth dynamics of a decagonal quasicrystal and its approximant `X' phase are considered. Various similarities and differences are elucidated.

Principles of weakly ordered domains in intermetallics: the cooperative effects of atomic packing and electronics in Fe₂Al₅

The Fe₂Al₅ structure is remarkable among intermetallic phases for its channels of weakly ordered Al atoms. This article traces the origins of these channels to the cooperative effects of soft atomic motions dictated by chemical pressure quadrupoles and preferred electron concentrations.

Full real-space analysis of a dodecagonal quasicrystal

Analysis of a dodecagonal quasicrystal based on 8100 vertices from atomically resolved scanning tunnelling microscopy has been carried out. A detailed frequency and orientational analysis is presented for the triangle–square–rhomb tiling of a BaTiO₃-derived quasicrystal.

Bonding network and stability of clusters: the case study of Al₁₃TM₄ pseudo-tenfold surfaces

The physical significance of clusters in Al₁₃TM₄ compounds is invesitgated through ab initio methods based on density functional theory.

Monoclinic sphere packings. III. Trivariant lattice complexes of P2/c and P2₁/c

All homogeneous sphere packings were derived that refer to the trivariant lattice complexes of monoclinic space groups of types P2/c and P2₁/c.

Resolving 500 nm axial separation by multi-slice X-ray ptychography

Combining multi-slice ptychography with multi-modality scanning probe microscopy reconstructs two planes of nanostructures separated by 500 nm with sub-20 nm lateral resolution, assisted by simultaneously measured fluorescence maps for decoupling low-spatial-frequency features.

Grazing-incidence small-angle X-ray scattering study of correlated lateral density fluctuations in W/Si multilayers

An inhomogeneity of material in W/Si multilayer structures was studied with grazing-incidence small-angle X-ray scattering. The experimental study revealed lateral density fluctuations in the Si spacer layers.

Phason-flips refinement of and multiple-scattering correction for the d-AlCuRh quasicrystal

The structure factor with lattice phason flips for a decagonal quasicrystal is derived. Bias in the calculated diffraction data is most likely to be a consequence of multiple scattering.

Absorption and secondary scattering of X-rays with an off-axis small beam for a cylindrical sample geometry

Absorption and secondary scattering corrections for a cylindrical sample geometry are developed for the case when the incident beam is smaller than the sample and, in general, off-center from the cylinder.

Aspects of the topology of actinide atom substructures in crystal structures and the concept of antiliquid

Consideration of the maximum space-filling principle and the short-range (local) and long-range (translational) order using Voronoi–Dirichlet polyhedra reveals the most probable number of neighboring atoms and the concept of antiliquid.

Group-theoretical analysis of 1:3 A-site-ordered perovskite formation

A group-theoretical analysis of 1:3 A-site-ordered perovskite structures is reported.

Extension of the transferable aspherical pseudoatom data bank for the comparison of molecular electrostatic potentials in structure–activity studies

The transferable aspherical pseudoatom data bank, UBDB2018, is extended with over 130 new atom types present in small and biological molecules of importance in biology and chemistry. UBDB2018 can be used to enhance the physical meaning of molecular electrostatic potentials which can be utilized in, amongst other fields, drug discovery studies.

Thermoelectric transport properties in magnetically ordered crystals. Corrigendum and addenda

A correction and additions concerning the limiting point groups are made to the article by Grimmer [Acta Cryst. (2017), A73, 333–345].

Aperiodic Order: Volume 2, Crystallography and Almost Periodicity