Report of the Executive Committee for 2020
The report of the Executive Committee for 2020 is presented. (Source: Acta Crystallographica Section A)
Source: Acta Crystallographica Section A - December 22, 2021 Category: Chemistry Authors: Ashcroft, A.T. Tags: International Union of Crystallography IUCr Executive Committee Source Type: research
On the frequency module of the hull of a primitive substitution tiling
Understanding the properties of tilings is of increasing relevance to the study of aperiodic tilings and tiling spaces. This work considers the statistical properties of the hull of a primitive substitution tiling, where the hull is the family of all substitution tilings with respect to the substitution. A method is presented on how to arrive at the frequency module of the hull of a primitive substitution tiling (the minimal {\bb Z}-module, where {\bb Z} is the set of integers) containing the absolute frequency of each of its patches. The method involves deriving the tiling's edge types and vertex stars; in the process, a ...
Source: Acta Crystallographica Section A - December 22, 2021 Category: Chemistry Authors: Say-awen, A.L.D. Frettl ö h, D. De Las Pe ñ as, M.L.A.N. Tags: frequency module primitive substitution tilings aperiodic tilings quasicrystals research papers Source Type: research
Uwe Grimm (1963 – 2021)
(Source: Acta Crystallographica Section A)
Source: Acta Crystallographica Section A - December 20, 2021 Category: Chemistry Authors: Baake, M. McGrath, R. R ö mer, R.A. Tags: obituary quasicrystals quasi-periodic systems aperiodic order group theory obituaries Source Type: research
Numerical Problems in Crystallography. By M. A. Wahab. Springer, 2021. Hardcover, pp. xv + 387. ISBN 9789811597534. Price EUR 83.19.
(Source: Acta Crystallographica Section A)
Source: Acta Crystallographica Section A - December 20, 2021 Category: Chemistry Authors: Nespolo, M. Tags: book review crystallographic computing book reviews Source Type: research
The intrinsic group – subgroup structures of the Diamond and Gyroid minimal surfaces in their conventional unit cells
The intrinsic, hyperbolic crystallography of the Diamond and Gyroid minimal surfaces in their conventional unit cells is introduced and analysed. Tables are constructed of symmetry subgroups commensurate with the translational symmetries of the surfaces as well as group – subgroup lattice graphs. (Source: Acta Crystallographica Section A)
Source: Acta Crystallographica Section A - December 20, 2021 Category: Chemistry Authors: Pedersen, M.C. Robins, V. Hyde, S.T. Tags: minimal surfaces hyperbolic geometry symmetry groups subgroup lattices conventional unit cells short communications Source Type: research
Chiral spiral cyclic twins
A formula is presented for the generation of chiral m-fold multiply twinned two-dimensional point sets of even twin modulus m> 6 from an integer inclination sequence; in particular, it is discussed for the first three non-degenerate cases m = 8, 10, 12, which share a connection to the aperiodic crystallography of axial quasicrystals exhibiting octagonal, decagonal and dodecagonal long-range orientational order and symmetry. (Source: Acta Crystallographica Section A)
Source: Acta Crystallographica Section A - December 20, 2021 Category: Chemistry Authors: Hornfeck, W. Tags: chiral spiral cyclic twins research papers Source Type: research
Effects of Voigt diffraction peak profiles on the pair distribution function
Powder diffraction and pair distribution function (PDF) analysis are well established techniques for investigation of atomic configurations in crystalline materials, and the two are related by a Fourier transformation. In diffraction experiments, structural information, such as crystallite size and microstrain, is contained within the peak profile function of the diffraction peaks. However, the effects of the PXRD (powder X-ray diffraction) peak profile function on the PDF are not fully understood. Here, all the effects from a Voigt diffraction peak profile are solved analytically, and verified experimentally through a hig...
Source: Acta Crystallographica Section A - December 20, 2021 Category: Chemistry Authors: Beyer, J. Roth, N. Brummerstedt Iversen, B. Tags: pair distribution function peak profile Voigt function strain effects size effects research papers Source Type: research
A new method for lattice reduction using directional and hyperplanar shearing
A geometric method of lattice reduction based on cycles of directional and hyperplanar shears is presented. The deviation from cubicity at each step of the reduction is evaluated by a parameter called `basis rhombicity' which is the sum of the absolute values of the elements of the metric tensor associated with the basis. The levels of reduction are quite similar to those obtained with the Lenstra – Lenstra – Lov á sz (LLL) algorithm, at least up to the moderate dimensions that have been tested (lower than 20). The method can be used to reduce unit cells attached to given hyperplanes. (Source: Acta Crystallographica Section A)
Source: Acta Crystallographica Section A - December 20, 2021 Category: Chemistry Authors: Cayron, C. Tags: lattice reduction hyperplane left inverse algorithm research papers Source Type: research
Prices of IUCr journals
(Source: Acta Crystallographica Section A)
Source: Acta Crystallographica Section A - October 29, 2021 Category: Chemistry Authors: Ashcroft, A.T. Tags: prices of journals international union of crystallography Source Type: research
On single-crystal total scattering data reduction and correction protocols for analysis in direct space
Data reduction and correction steps and processed data reproducibility in the emerging single-crystal total-scattering-based technique of three-dimensional differential atomic pair distribution function (3D- Δ PDF) analysis are explored. All steps from sample measurement to data processing are outlined using a crystal of CuIr2S4 as an example, studied in a setup equipped with a high-energy X-ray beam and a flat-panel area detector. Computational overhead as pertains to data sampling and the associated data-processing steps is also discussed. Various aspects of the final 3D- Δ PDF reproducibility are explicitly tested by ...
Source: Acta Crystallographica Section A - October 29, 2021 Category: Chemistry Authors: Koch, R.J. Roth, N. Liu, Y. Ivashko, O. Dippel, A.-C. Petrovic, C. Iversen, B.B. Zimmermann, M. v. Bozin, E.S. Tags: pair distribution function analysis PDF analysis single-crystal 3D differential PDF total scattering data reduction CuIr2S4 research papers Source Type: research
Vanishing of the atomic form factor derivatives in non-spherical structural refinement – a key approximation scrutinized in the case of Hirshfeld atom refinement
When calculating derivatives of structure factors, there is one particular term (the derivatives of the atomic form factors) that will always be zero in the case of tabulated spherical atomic form factors. What happens if the form factors are non-spherical? The assumption that this particular term is very close to zero is generally made in non-spherical refinements (for example, implementations of Hirshfeld atom refinement or transferable aspherical atom models), unless the form factors are refinable parameters (for example multipole modelling). To evaluate this general approximation for one specific method, a numerical di...
Source: Acta Crystallographica Section A - October 29, 2021 Category: Chemistry Authors: Midgley, L. Bourhis, L.J. Dolomanov, O.V. Grabowsky, S. Kleemiss, F. Puschmann, H. Peyerimhoff, N. Tags: quantum crystallography refinement non-spherical form factors research papers Source Type: research
Parameterization of magnetic vector potentials and fields for efficient multislice calculations of elastic electron scattering
The multislice method, which simulates the propagation of the incident electron wavefunction through a crystal, is a well established method for analysing the multiple scattering effects that an electron beam may undergo. The inclusion of magnetic effects into this method proves crucial towards simulating enhanced magnetic interaction of vortex beams with magnetic materials, calculating magnetic Bragg spots or searching for magnon signatures, to name a few examples. Inclusion of magnetism poses novel challenges to the efficiency of the multislice method for larger systems, especially regarding the consistent computation of...
Source: Acta Crystallographica Section A - October 29, 2021 Category: Chemistry Authors: Lyon, K. Rusz, J. Tags: magnetism multislice parameterization simulation DFT research papers Source Type: research
X-ray molecular orbital analysis. II. Application to diformohydrazide, (NHCHO)2
The molecular orbitals (MOs) of diformohydrazide have been determined from the electron density measured by X-ray diffraction. The experimental and refinement procedures are explained in detail and the validity of the obtained MOs is assessed from the crystallographic point of view. The X-ray structure factors were measured at 100 K by a four-circle diffractometer avoiding multiple diffraction, the effect of which on the structure factors is comparable to two-centre structure factors. There remained no significant peaks on the residual density map and the R factors reduced significantly. Among the 788 MO coefficients, ...
Source: Acta Crystallographica Section A - October 4, 2021 Category: Chemistry Authors: Tanaka, K. Wasada-Tsutsui, Y. Tags: X-ray molecular orbital analysis XMO analysis electron density molecular orbitals diformohydrazide multiple diffraction hydrogen bonds research papers Source Type: research
The wavevector star channel and symmetry group
The concepts of `wavevector star channel' and `wavevector star channel group' are newly defined, which allow the effective study of phase transitions considering directly the translational symmetry breaking in crystals. A method is suggested by which the wavevector star channels can be found using the image of the representation of the translational group. According to this method, the wavevector star channels are found for the 80 Lifschitz stars in the reciprocal lattice. The wavevector star channel group is defined as the set of symmetry elements of the parent phase which leave the star channel invariant, and the wavevec...
Source: Acta Crystallographica Section A - September 29, 2021 Category: Chemistry Authors: Kim, I.H. Sin, K.R. Pak, J.O. Kim, I.H. Jang, K.O. Kim, C.J. Tags: wavevector star channels wavevector star channel groups translational symmetry breaking phase transitions lead calcium titanate Pb1 − xCaxTiO3 PCT research papers Source Type: research
Layer groups: Brillouin-zone and crystallographic databases on the Bilbao Crystallographic Server
The section of the Bilbao Crystallographic Server (https://www.cryst.ehu.es/) dedicated to subperiodic groups contains crystallographic and Brillouin-zone databases for the layer groups. The crystallographic databases include the generators/general positions (GENPOS), Wyckoff positions (WYCKPOS) and maximal subgroups (MAXSUB). The Brillouin-zone database (LKVEC) offers k-vector tables and Brillouin-zone figures of all 80 layer groups which form the background of the classification of their irreducible representations. The symmetry properties of the wavevectors are described applying the so-called reciprocal-space-group app...
Source: Acta Crystallographica Section A - September 24, 2021 Category: Chemistry Authors: de la Flor, G. Souvignier, B. Madariaga, G. Aroyo, M.I. Tags: Bilbao Crystallographic Server layer groups Brillouin-zone database research papers Source Type: research
