On the determination of dense coincidence site lattice planes
The concept of coincidence site lattice (CSL) is used in descriptions of geometry of some intercrystalline boundaries. In face-centered cubic and body-centered cubic metals, atoms are located at the nodes of lattices, and results concerning lattice nodes are applicable to atomic sites. One of the criteria for special boundary configurations is that the boundary passes through a plane with a high density of coinciding atomic sites. Hence, there is an issue of identification of such planes. This paper describes a simple and reliable method for determining the planes with high densities of coinciding lattice nodes. The key el...
Source: Acta Crystallographica Section A - October 21, 2022 Category: Chemistry Authors: Morawiec, A. Tags: crystal lattice coincidence site lattice intercrystalline interface Hermite normal form Niggli reduction research papers Source Type: research
On single-crystal total scattering data reduction and correction protocols for analysis in direct space. Corrigendum
The name of the third author of the article by Koch et al. [Acta Cryst. (2021). A77, 611 – 636] is corrected. (Source: Acta Crystallographica Section A)
Source: Acta Crystallographica Section A - October 10, 2022 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 addenda and errata Source Type: research
Simulating dark-field X-ray microscopy images with wavefront propagation techniques
Dark-field X-ray microscopy is a diffraction-based synchrotron imaging technique capable of imaging defects in the bulk of extended crystalline samples. Numerical simulations are presented of image formation in such a microscope using numerical integration of the dynamical Takagi – Taupin equations and wavefront propagation. The approach is validated by comparing simulated images with experimental data from a near-perfect single crystal of diamond containing a single stacking-fault defect in the illuminated volume. (Source: Acta Crystallographica Section A)
Source: Acta Crystallographica Section A - October 10, 2022 Category: Chemistry Authors: Carlsen, M. Detlefs, C. Yildirim, C. R æ der, T. Simons, H. Tags: diffraction imaging dynamical diffraction simulation research papers Source Type: research
Extending the novel | ρ |-based phasing algorithm to the solution of anomalous scattering substructures from SAD data of protein crystals
Owing to the importance of the single-wavelength anomalous diffraction (SAD) technique, the recently developed | ρ |-based phasing algorithm (SM,| ρ |) incorporating the inner-pixel preservation (ipp) procedure [Rius& Torrelles (2021). Acta Cryst A77, 339 – 347] has been adapted to the determination of anomalous scattering substructures and its applicability tested on a series of 12 representative experimental data sets, mostly retrieved from the Protein Data Bank. To give an idea of the suitability of the data sets, the main indicators measuring their quality are also given. The dominant anomalous scatterers are eithe...
Source: Acta Crystallographica Section A - October 10, 2022 Category: Chemistry Authors: Rius, J. Torrelles, X. Tags: SM, ρ phasing algorithm SMAR phasing ipp density modification SAD-SMAR -based direct methods structure solution research papers Source Type: research
Time-dependent dynamical Bragg diffraction in deformed crystals by the beam propagation method
This paper describes how to efficiently solve time-dependent X-ray dynamic diffraction problems in distorted crystals with a fast Fourier transform based beam propagation method. Examples are given of using the technique to simulate the propagation of X-ray beams in deformed crystals in space and time domains relevant to the cavity-based X-ray free-electron lasers and X-ray free-electron laser self-seeding systems. (Source: Acta Crystallographica Section A)
Source: Acta Crystallographica Section A - October 10, 2022 Category: Chemistry Authors: Krzywinski, J. Halavanau, A. Tags: dynamical diffraction Fourier optics beam propagation method research papers Source Type: research
Call for nominations for the W. H. & W. L. Bragg Prize
(Source: Acta Crystallographica Section A)
Source: Acta Crystallographica Section A - August 30, 2022 Category: Chemistry Authors: Stanley, A.M. Tags: W. H. & W. L. Bragg Prize International Union of Crystallography Source Type: research
Call for nominations for the Ewald Prize
(Source: Acta Crystallographica Section A)
Source: Acta Crystallographica Section A - August 30, 2022 Category: Chemistry Authors: Stanley, A.M. Tags: Ewald Prize International Union of Crystallography Source Type: research
Local groups in Delone sets in the Euclidean space
A Delone (Delaunay) set is a uniformly discrete and relatively dense set of points located in space, and is a natural mathematical model of the set of atomic positions of any solid, whether it is crystalline, quasi-crystalline or amorphous. A Delone set has two positive parameters: r is the packing radius and R is the covering radius. The value 2r can be interpreted as the minimum distance between points of the set. The covering radius R is the radius of the biggest `empty' ball, i.e. the radius of the biggest ball containing no points from the set. The central concept of this article is the so-called local group at a poin...
Source: Acta Crystallographica Section A - August 30, 2022 Category: Chemistry Authors: Dolbilin, N. Shtogrin, M. Tags: Delone sets Delaunay sets clusters cluster groups crystal kernel 2R-isometrical Delone sets research papers Source Type: research
Towards a machine-readable literature: finding relevant papers based on an uploaded powder diffraction pattern
A prototype application for machine-readable literature is investigated. The program is called pyDataRecognition and serves as an example of a data-driven literature search, where the literature search query is an experimental data set provided by the user. The user uploads a powder pattern together with the radiation wavelength. The program compares the user data to a database of existing powder patterns associated with published papers and produces a rank ordered according to their similarity score. The program returns the digital object identifier and full reference of top-ranked papers together with a stack plot of the...
Source: Acta Crystallographica Section A - August 19, 2022 Category: Chemistry Authors: Ö zer, B. Karlsen, M.A. Thatcher, Z. Lan, L. McMahon, B. Strickland, P.R. Westrip, S.P. Sang, K.S. Billing, D.G. Ravnsbaek, D.B. Billinge, S.J.L. Tags: machine-readable scientific literature data-driven literature search powder diffraction data similarity CIF research papers Source Type: research
Pure discrete spectrum and regular model sets on some non-unimodular substitution tilings
Substitution tilings with pure discrete spectrum are characterized as regular model sets whose cut-and-project scheme has an internal space that is a product of a Euclidean space and a profinite group. Assumptions made here are that the expansion map of the substitution is diagonalizable and its eigenvalues are all algebraically conjugate with the same multiplicity. A difference from the result of Lee et al. [Acta Cryst. (2020), A76, 600 – 610] is that unimodularity is no longer assumed in this paper. (Source: Acta Crystallographica Section A)
Source: Acta Crystallographica Section A - August 12, 2022 Category: Chemistry Authors: Lee, J.-Y. Tags: pure discrete spectrum regular model sets non-unimodular substitution Pisot family substitution Meyer sets research papers Source Type: research
A simple formula for determining nanoparticle size distribution by combining small-angle X-ray scattering and diffraction results
X-ray scattering and diffraction phenomena are widely used as analytical tools in nanoscience. Size discrepancies between the two phenomena are commonly observed in crystalline nanoparticle systems. The root of the problem is that each phenomenon is affected by size distribution differently, causing contrasting shifts between the two methods. Once understood, the previously discrepant results lead to a simple formula for obtaining the nanoparticle size distribution. (Source: Acta Crystallographica Section A)
Source: Acta Crystallographica Section A - August 5, 2022 Category: Chemistry Authors: Morelh ã o, S.L. Kycia, S.W. Tags: nanocrystalline materials nanoparticle size distribution X-ray scattering and diffraction Scherrer equation Guinier approximation short communications Source Type: research
Crystallographic phase retrieval method for liquid crystal bicontinuous phases: indicator-based method
An indicator-based crystallographic phase retrieval method has been developed for diffraction data of bicontinuous cubic phases of lyotropic liquid crystals. Such liquid crystals have large structural disorder; the number of independent Bragg reflections that can be observed is limited. This paper proposes two indicators to identify plausible combination(s) of crystallographic phases, i.e. electron-density distribution. The indicators are based on the characteristics of the liquid crystals: amphiphilic molecules diffuse mainly in the direction parallel to polar – nonpolar interfaces and the electron density in the direct...
Source: Acta Crystallographica Section A - July 28, 2022 Category: Chemistry Authors: Oka, T. Tags: lyotropic liquid crystals triply periodic minimal surfaces crystallographic phase retrieval research papers Source Type: research
Origin of irregular X-ray mirage fringes from a bent, thin crystal
The dynamical theory of diffraction is used to analyse irregular X-ray mirage interference fringes observed in Si220 X-ray reflection topography from a weakly bent, thin crystal due to gravity. The origin of the irregular fringes is attributed to the interference between mirage diffracted beams and a reflected beam from the back surface, which is a new type of interference fringe. The irregular fringes are reproduced by calculating the reflected intensities numerically. The effects of absorption and thermal vibration are quite important for the reproduction. The result shows that the interference fringes depend on the stra...
Source: Acta Crystallographica Section A - July 28, 2022 Category: Chemistry Authors: Fukamachi, T. Kawamura, T. Tags: interference fringes mirage fringes bent crystal dynamical theory of X-ray diffraction research papers Source Type: research
Semi-analytic theory of multiphonon effects on the static structure factors of warm solids
A semi-analytic formula for the temperature-dependent static structure factor S(k) of polycrystalline and amorphous solids applicable to the entire wavenumber (k) range is derived. The formula describes thermal diffuse scattering due to multiphonon processes entirely by a single kernel function without resorting to the standard perturbation expansion. It is analytically proven that S(k → 0) is determined from the one-phonon term, whereas the asymptotic limit S(k → ∞ ) = 1 can be reproduced through a Gaussian integral of the multiphonon term. The formula also reveals that an enhancement of the one-phonon scattering in...
Source: Acta Crystallographica Section A - July 21, 2022 Category: Chemistry Authors: Kitamura, H. Tags: static structure factor thermal diffuse scattering multiphonon processes research papers Source Type: research
A finite difference scheme for integrating the Takagi – Taupin equations on an arbitrary orthogonal grid
Calculating dynamical diffraction patterns for X-ray diffraction imaging techniques requires numerical integration of the Takagi – Taupin equations. This is usually performed with a simple, second-order finite difference scheme on a sheared computational grid in which two of the axes are aligned with the wavevectors of the incident and scattered beams. This dictates, especially at low scattering angles, an oblique grid of uneven step sizes. Here a finite difference scheme is presented that carries out this integration in slab-shaped samples on an arbitrary orthogonal grid by implicitly utilizing Fourier interpolation. Th...
Source: Acta Crystallographica Section A - July 21, 2022 Category: Chemistry Authors: Carlsen, M. Simons, H. Tags: dynamical diffraction X-ray topography research papers Source Type: research
