Isogonal non-crystallographic periodic graphs based on knotted sodalite cages
This work considers non-crystallographic periodic nets obtained from multiple identical copies of an underlying crystallographic net by adding or flipping edges so that the result is connected. Such a structure is called a `ladder' net here because the 1-periodic net shaped like an ordinary (infinite) ladder is a particularly simple example. It is shown how ladder nets with no added edges between layers can be generated from tangled polyhedra. These are simply related to the zeolite nets SOD, LTA and FAU. They are analyzed using new extensions of algorithms in the program Systre that allow unambiguous identification of loc...
Source: Acta Crystallographica Section A - October 29, 2020 Category: Chemistry Authors: Delgado-Friedrichs, O. O'Keeffe, M. Treacy, M.M.J. Tags: knotted zeolite frameworks linked zeolite frameworks non-crystallographic symmetry Systre research papers Source Type: research
Indexing of diffraction patterns for determination of crystal orientations
The task of determining the orientations of crystals is usually performed by indexing reflections detected on diffraction patterns. The well known underlying principle of indexing methods is universal: they are based on matching experimental scattering vectors to some vectors of the reciprocal lattice. Despite this, the standard attitude has been to devise algorithms applicable to patterns of a particular type. This paper provides a broader perspective. A general approach to indexing of diffraction patterns of various types is presented. References are made to formally similar problems in other research fields, e.g. in com...
Source: Acta Crystallographica Section A - October 29, 2020 Category: Chemistry Authors: Morawiec, A. Tags: diffraction crystal orientation indexing crystallographic computing research papers Source Type: research
Algorithms for target transformations of lattice basis vectors
Simple algorithms are proposed for the transformation of lattice basis vectors to a specific target. In the first case, one of the new basis vectors is aligned to a predefined lattice direction, while in the second case, two of the new basis vectors are brought to a lattice plane with predefined Miller indices. The multi-dimensional generalization of the algorithm is available in the supporting materials. The algorithms are useful for such crystallographic operations as simulation of zone planes (i.e. geometry of electron diffraction patterns) or transformation of a unit cell for surface or cleavage energy calculations. Th...
Source: Acta Crystallographica Section A - October 29, 2020 Category: Chemistry Authors: Gorfman, S. Tags: crystal lattice transformations lattice planes zones research papers Source Type: research
Embedding parallelohedra into primitive cubic networks and structural automata description
The main goal of the paper is to contribute to the agenda of developing an algorithmic model for crystallization and measuring the complexity of crystals by constructing embeddings of 3D parallelohedra into a primitive cubic network (pcu net). It is proved that any parallelohedron P as well as tiling by P, except the rhombic dodecahedron, can be embedded into the 3D pcu net. It is proved that for the rhombic dodecahedron embedding into the 3D pcu net does not exist; however, embedding into the 4D pcu net exists. The question of how many ways the embedding of a parallelohedron can be constructed is answered. For each parall...
Source: Acta Crystallographica Section A - October 23, 2020 Category: Chemistry Authors: Bouniaev, M.M. Krivovichev, S.V. Tags: parallelohedra crystalline structures primitive cubic nets deterministic finite automata structural automata research papers Source Type: research
Electron image contrast analysis of mosaicity in rutile nanocrystals using direct electron detection
Direct electron detection provides high detective quantum efficiency, significantly improved point spread function and fast read-out which have revolutionized the field of cryogenic electron microscopy. However, these benefits for high-resolution electron microscopy (HREM) are much less exploited, especially for in situ study where major impacts on crystallographic structural studies could be made. By using direct detection in electron counting mode, rutile nanocrystals have been imaged at high temperature inside an environmental transmission electron microscope. The improvements in image contrast are quantified by compari...
Source: Acta Crystallographica Section A - October 23, 2020 Category: Chemistry Authors: Yoon, A. Shao, Y.-T. Howe, J. Zuo, J.-M. Tags: rutile nanocrystals mosaicity quantitative HREM Stobbs factor research papers Source Type: research
A Journey into Reciprocal Space: A Crystallographer's Perspective. By A. M. Glazer. Morgan & Claypool, 2017. Paperback, pp. 190. Price USD 55.00. ISBN 9781681746203.
(Source: Acta Crystallographica Section A)
Source: Acta Crystallographica Section A - October 19, 2020 Category: Chemistry Authors: St ö ger,B. Tags: book review reciprocal space book reviews Source Type: research
Similarity isometries of point packings
In this study, the notion of similarity isometries is extended to point packings. A characterization for the similarity isometries of point packings is provided and the corresponding similar subpackings are identified. Planar examples are discussed, namely the 1 × 2 rectangular lattice and the hexagonal packing (or honeycomb lattice). Finally, similarity isometries of point packings about points different from the origin are considered by studying similarity isometries of shifted point packings. In particular, similarity isometries of a certain shifted hexagonal packing are computed and compared with those of the ...
Source: Acta Crystallographica Section A - October 19, 2020 Category: Chemistry Authors: Arias, J.C.H. Loquias, M.J.C. Tags: similarity isometries similar sublattices point packings hexagonal packings research papers Source Type: research
Prices of IUCr journals
(Source: Acta Crystallographica Section A)
Source: Acta Crystallographica Section A - October 12, 2020 Category: Chemistry Authors: Ashcroft, A.T. Tags: prices of journals international union of crystallography Source Type: research
Effect of radiation damage and illumination variability on signal-to-noise ratio in X-ray free-electron laser single-particle imaging
The deterioration of both the signal-to-noise ratio and the spatial resolution in the electron-density distribution reconstructed from diffraction intensities collected at different orientations of a sample is analysed theoretically with respect to the radiation damage to the sample and the variations in the X-ray intensities illuminating different copies of the sample. The simple analytical expressions and numerical estimates obtained for models of radiation damage and incident X-ray pulses may be helpful in planning X-ray free-electron laser (XFEL) imaging experiments and in analysis of experimental data. This approach t...
Source: Acta Crystallographica Section A - October 12, 2020 Category: Chemistry Authors: Gureyev, T.E. Kozlov, A. Morgan, A.J. Martin, A.V. Quiney, H.M. Tags: XFEL imaging radiation damage signal-to-noise ratio X-ray free-electron laser imaging spatial resolution research papers Source Type: research
A flexible and standalone forward simulation model for laboratory X-ray diffraction contrast tomography
Laboratory X-ray diffraction contrast tomography (LabDCT) has recently been developed as a powerful technique for non-destructive mapping of grain microstructures in bulk materials. As the grain reconstruction relies on segmentation of diffraction spots, it is essential to understand the physics of the diffraction process and resolve all the spot features in detail. To this aim, a flexible and standalone forward simulation model has been developed to compute the diffraction projections from polycrystalline samples with any crystal structure. The accuracy of the forward simulation model is demonstrated by good agreements in...
Source: Acta Crystallographica Section A - September 17, 2020 Category: Chemistry Authors: Fang, H. Juul Jensen, D. Zhang, Y. Tags: 3D grain mapping diffraction contrast tomography X-ray diffraction forward simulation grain reconstruction research papers Source Type: research
Fast analytical evaluation of intermolecular electrostatic interaction energies using the pseudoatom representation of the electron density. III. Application to crystal structures via the Ewald and direct summation methods
The previously reported exact potential and multipole moment (EP/MM) method for fast and accurate evaluation of the intermolecular electrostatic interaction energies using the pseudoatom representation of the electron density [Volkov, Koritsanszky& Coppens (2004). Chem. Phys. Lett. 391, 170 – 175; Nguyen, Kisiel& Volkov (2018). Acta Cryst. A74, 524 – 536; Nguyen& Volkov (2019). Acta Cryst. A75, 448 – 464] is extended to the calculation of electrostatic interaction energies in molecular crystals using two newly developed implementations: (i) the Ewald summation (ES), which includes interactions up to the hexadecapolar...
Source: Acta Crystallographica Section A - September 17, 2020 Category: Chemistry Authors: Nguyen, D. Macchi, P. Volkov, A. Tags: electrostatic interaction energy charge density pseudoatom model ö wdin α -function multipole expansion Ewald summation lattice sums research papers Source Type: research
On the Σ classes in E6
In E6, the cone of positive definite quadratic forms is subdivided into Σ s subcones and its equivalence classes {\cal E}_{\Sigma _s} are determined for s = 0 – 3, and 18 – 21. (Source: Acta Crystallographica Section A)
Source: Acta Crystallographica Section A - August 24, 2020 Category: Chemistry Authors: Engel, P. Tags: translation lattices parallelohedra cone of positive quadratic forms Sigma classes research papers Source Type: research
Tilings by hexagonal prisms and embeddings into primitive cubic networks
All possible combinatorial embeddings into primitive cubic networks of arbitrary tilings of 3D space by pairwise congruent and parallel regular hexagonal prisms are discussed and classified. (Source: Acta Crystallographica Section A)
Source: Acta Crystallographica Section A - August 20, 2020 Category: Chemistry Authors: Bouniaev, M.M. Dolbilin, N.P. Shtogrin, M.I. Tags: tilings primitive cubic networks parallelohedra embeddings hexagonal prisms short communications Source Type: research
Isogonal weavings on the sphere: knots, links, polycatenanes
Mathematical knots and links are described as piecewise linear – straight, non-intersecting sticks meeting at corners. Isogonal structures have all corners related by symmetry (`vertex'-transitive). Corner- and stick-transitive structures are termed regular. No regular knots are found. Regular links are cubic or icosahedral and a complete account of these (36 in number) is given, including optimal (thickest-stick) embeddings. Stick 2-transitive isogonal structures are again cubic and icosahedral and also encompass the infinite family of torus knots and links. The major types of these structures are identified and reporte...
Source: Acta Crystallographica Section A - August 20, 2020 Category: Chemistry Authors: O'Keeffe, M. Treacy, M.M.J. Tags: weaves knots links catenanes research papers Source Type: research
Pure discrete spectrum and regular model sets in d-dimensional unimodular substitution tilings
Primitive substitution tilings on {\bb R}^d whose expansion maps are unimodular are considered. It is assumed that all the eigenvalues of the expansion maps are algebraic conjugates with the same multiplicity. In this case, a cut-and-project scheme can be constructed with a Euclidean internal space. Under some additional condition, it is shown that if the substitution tiling has pure discrete spectrum, then the corresponding representative point sets are regular model sets in that cut-and-project scheme. (Source: Acta Crystallographica Section A)
Source: Acta Crystallographica Section A - August 20, 2020 Category: Chemistry Authors: Lee, D.-I. Akiyama, S. Lee, J.-Y. Tags: Pisot family substitution tilings pure discrete spectrum regular model sets Meyer sets rigidity research papers Source Type: research
