Acta Crystallographica Section A

Items from 1 to 20 out of 303 results

article

X‐ray constrained unrestricted Hartree–Fock and Douglas–Kroll–Hess wavefunctions

Martin Hudák, Dylan Jayatilaka, Lucia Perašínová, Stanislav Biskupič, more

Acta Crystallographica Section A > 66 > 1 > 78 - 92

The extension of the X‐ray constrained (XC) wavefunction approach to open‐shell systems using the unrestricted Hartree–Fock formalism is reported. The XC method is also extended to include relativistic effects using the scalar second‐order Douglas–Kroll–Hess approach. The relativistic effects on the charge and spin density on two model compounds containing the copper and iron atom are reported. The...

article

A new approach to calculating powder diffraction patterns based on the Debye scattering equation

Noel William Thomas

Acta Crystallographica Section A > 66 > 1 > 64 - 77

A new method is defined for the calculation of X‐ray and neutron powder diffraction patterns from the Debye scattering equation (DSE). Pairwise atomic interactions are split into two contributions, the first from lattice‐pair vectors and the second from cell‐pair vectors. Since the frequencies of lattice‐pair vectors can be directly related to crystallite size, application of the DSE is thereby extended...

article

Report of the Executive Committee for 2008

Acta Crystallographica Section A > 66 > 1 > 98 - 126

article

Molecular crystal global phase diagrams. II. Reference lattices

Richard B. McClurg, J. Brandon Keith

Acta Crystallographica Section A > 66 > 1 > 38 - 49

In the first part of this series [Keith et al. (2004). Cryst. Growth Des.4, 1009–1012; Mettes et al. (2004). Acta Cryst. A60, 621–636], a method was developed for constructing global phase diagrams (GPDs) for molecular crystals in which crystal structure is presented as a function of intermolecular potential parameters. In that work, a face‐centered‐cubic center‐of‐mass lattice was arbitrarily adopted...

article

Molecular crystal global phase diagrams. III. Sufficient parameter space determination

J. Brandon Keith, Richard B. McClurg

Acta Crystallographica Section A > 66 > 1 > 50 - 63

In previous parts of this series [Mettes et al. (2004). Acta Cryst. A60, 621–636; McClurg & Keith (2010). Acta Cryst. A66, 38–49] a method for constructing global phase diagrams (GPDs) for molecular crystals was developed and the method was applied to single‐component ordered crystal structures of tetrahedral molecules. GPDs are useful for visualizing what types of crystal structures a given molecule...

article

Effect of convergent beam semiangle on image intensity in HAADF STEM images

Koji Kuramochi, Yasutoshi Kotaka, Takashi Yamazaki, Masahiro Ohtsuka, more

Acta Crystallographica Section A > 66 > 1 > 10 - 16

In this study, we experimentally and theoretically show that the intensities of bright spots in a spherical aberration (C_s)‐uncorrected high‐angle annular dark‐field (HAADF) scanning transmission electron microscope (STEM) image of [011]‐oriented Co₃O₄, which has two different numbers of Co atoms in the projected atomic columns, are reversed with increasing sample thickness. However, C_s‐corrected...

article

Reconstruction from a single diffraction pattern of azimuthally projected electron density of molecules aligned parallel to a single axis

D. K. Saldin, V. L. Shneerson, D. Starodub, J. C. H. Spence

Acta Crystallographica Section A > 66 > 1 > 32 - 37

Diffraction from the individual molecules of a molecular beam, aligned parallel to a single axis by a strong electric field or other means, has been proposed as a means of structure determination of individual molecules. As in fiber diffraction, all the information extractable is contained in a diffraction pattern from incidence of the diffracting beam normal to the molecular alignment axis. The limited...

article

The birth of the European Crystallographic Committee (ECC) and of the European Crystallographic Meetings (ECMs)

André Authier

Acta Crystallographica Section A > 66 > 1 > 1 - 4

At ECM25, held in Istanbul, Turkey, on 16–21 August 2009, the 25th anniversary of the European Crystallographic Meetings was celebrated. In this article, it is recalled how the idea of coordinating international meetings on crystallography in Europe was put forward at a meeting held in Manchester, UK, in April 1971, and it is explained how the European Crystallographic Committee was established for...

article

Notes for authors 2010

Acta Crystallographica Section A > 66 > 1 > 128 - 132

article

Nominations for the Ewald Prize

Acta Crystallographica Section A > 66 > 1 > 127 - 127

article

Low‐angle scattering by cylindrical structures

Girija Bhushan Mitra

Acta Crystallographica Section A > 66 > 1 > 93 - 97

A theory of diffraction at small angles of scattering by a cylindrically constructed structure has been developed and general expressions for two‐ and three‐dimensional cylindrically curved crystallites have been obtained. Modified expressions have been derived for special cases of (a) a single arc of equiangularly spaced identical atoms, (b) several coaxial arcs each having an equal number of equiangularly...

article

The long‐wavelength limit of the structure factor of amorphous silicon and vitreous silica

Adam M. R. De Graff, M. F. Thorpe

Acta Crystallographica Section A > 66 > 1 > 22 - 31

Liquids are in thermal equilibrium and have a non‐zero structure factor = = in the long‐wavelength limit where is the number density, is the temperature, is the scattering vector and is the isothermal compressibility. The first part of this result involving the number (or density) fluctuations is a purely geometrical result and does not involve any assumptions about thermal equilibrium or...

article

A neutron interferometric measurement of a phase shift induced by Laue transmission

J. Springer, M. Zawisky, H. Lemmel, M. Suda

Acta Crystallographica Section A > 66 > 1 > 17 - 21

The phenomenon of a neutron phase shift due to Laue transmission in a perfect crystal blade is discussed. Quantitative measurements of this phase shift are presented in the vicinity of the Bragg condition well in agreement with numerical calculations. The phase shift shows a strong angular sensitivity and might constitute an interesting opportunity for precision measurements of fundamental quantities...

article

Dense quasicrystalline tilings by squares and equilateral triangles

Michael O'Keeffe, Michael M. J. Treacy

Acta Crystallographica Section A > 66 > 1 > 5 - 9

Dense square‐symmetry tilings of the plane by equilateral triangles and squares are described. Repeated substitution of a vertex of a tiling by groups of vertices leads asymptotically to a limiting density that is independent of the starting pattern and to a family of quasicrystalline patterns with 12‐fold symmetry. Diffraction patterns were computed by treating the vertices as point scatterers. As...

article

Analysis of time‐resolved X‐ray scattering data from solution‐state systems

Kristoffer Haldrup, Morten Christensen, Martin Meedom Nielsen

Acta Crystallographica Section A > 66 > 2 > 261 - 269

As ultrafast time‐resolved studies of liquid systems with the laser pump/X‐ray scattering probe method have come of age over the past decade, several groups have developed methods for the analysis of such X‐ray scattering data. The present article describes a method developed primarily with a focus on determining structural parameters in the excited states of medium‐sized molecules (~30 atoms) in...

article

Non‐equilibrium phonon dynamics studied by grazing‐incidence femtosecond X‐ray crystallography

S. L. Johnson, P. Beaud, E. Vorobeva, C. J. Milne, more

Acta Crystallographica Section A > 66 > 2 > 157 - 167

The timescales for structural changes in a single crystal of bismuth after excitation with an intense near‐infrared laser pulse are studied with femtosecond pump‐probe X‐ray diffraction. Changes in the intensity and reciprocal‐lattice vector of several reflections give quantitative information on the structure factor and lattice strain as a function of time, with a resolution of 200 fs. The results...

article

Excited‐state molecular structures captured by X‐ray transient absorption spectroscopy: a decade and beyond

Lin X. Chen, Xiaoyi Zhang, Jenny V. Lockard, Andrew B. Stickrath, more

Acta Crystallographica Section A > 66 > 2 > 240 - 251

Transient molecular structures along chemical reaction pathways are important for predicting molecular reactivity, understanding reaction mechanisms, as well as controlling reaction pathways. During the past decade, X‐ray transient absorption spectroscopy (XTA, or LITR‐XAS, laser‐initiated X‐ray absorption spectroscopy), analogous to the commonly used optical transient absorption spectroscopy, has...

article

Five‐dimensional crystallography

Marius Schmidt, Tim Graber, Robert Henning, Vukica Srajer

Acta Crystallographica Section A > 66 > 2 > 198 - 206

A method for determining a comprehensive chemical kinetic mechanism in macromolecular reactions is presented. The method is based on five‐dimensional crystallography, where, in addition to space and time, temperature is also taken into consideration and an analysis based on singular value decomposition is applied. First results of such a time‐resolved crystallographic study are presented. Temperature‐dependent...

article

Photoinduced structural dynamics of polar solids studied by femtosecond X‐ray diffraction

Thomas Elsaesser, Michael Woerner

Acta Crystallographica Section A > 66 > 2 > 168 - 178

Femtosecond X‐ray diffraction allows for real‐time mapping of structural changes in condensed matter on atomic length and timescales. Sequences of diffraction patterns provide both transient geometries and charge‐density maps of crystalline materials. This article reviews recent progress in this field, the main emphasis being on experimental work done with laser‐driven hard X‐ray sources. Both Bragg...

article

Dynamical structural science

E. Collet

Acta Crystallographica Section A > 66 > 2 > 133 - 134

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Keywords

X‐RAY DIFFRACTION (14)
DIRECT METHODS (10)
BOOK REVIEW (9)
PHASE PROBLEM (8)
DIFFUSE SCATTERING (7)
CHARGE DENSITY (6)
DYNAMICAL DIFFRACTION THEORY (6)
EDITORIAL (6)
OBITUARY (6)
POWDER DIFFRACTION (6)
ANISOTROPIC DISPLACEMENT PARAMETERS (5)
DYNAMICAL DIFFRACTION (5)
NEUTRON DIFFRACTION (5)
PRECESSION ELECTRON DIFFRACTION (5)
QUASICRYSTALS (5)
STRUCTURE DETERMINATION (5)
W. L. BRAGG (5)
CONVERGENT‐BEAM ELECTRON DIFFRACTION (4)
DEBYE–WALLER FACTORS (4)
DISORDER (4)
ELECTRON DIFFRACTION (4)
ELECTRON‐DENSITY MAPS (4)
FRIEDEL OPPOSITES (4)
MOLECULAR CRYSTALS (4)
PERIODIC NETS (4)
PRICES OF JOURNALS (4)
REPORT OF THE EXECUTIVE COMMITTEE (4)
STRUCTURAL DYNAMICS (4)
STRUCTURE FACTORS (4)
STRUCTURE SOLUTION (4)
TIME‐RESOLVED DIFFRACTION (4)
X‐RAY SCATTERING (4)
ANHARMONIC THERMAL MOTION (3)
CRYSTAL PACKING (3)
DISLOCATIONS (3)
EWALD PRIZE (3)
GRAZING‐INCIDENCE SMALL‐ANGLE X‐RAY SCATTERING (3)
INCOMMENSURATE PHASES (3)
MODULATED STRUCTURES (3)
MOLECULAR CRYSTALLOGRAPHY (3)
MOLECULAR DYNAMICS (3)
MULTIPLE DIFFRACTION (3)
NANOCRYSTALS (3)
NOTES FOR AUTHORS (3)
PHASE TRANSITIONS (3)
PHASING (3)
PHOTOCRYSTALLOGRAPHY (3)
PLANAR FAULTS (3)
POLARIZED X‐RAYS (3)
PROBABILITY DENSITY FUNCTIONS (3)
ROUGH SURFACES (3)
SHORT‐RANGE ORDER (3)
SPACE GROUPS (3)
STRUCTURE (3)
STRUCTURE FACTOR (3)
SYMMETRY (3)
TAKAGI–TAUPIN EQUATION (3)
VIRUS STRUCTURE (3)
AB INITIO STRUCTURE DETERMINATION (2)
AMINO ACIDS (2)
APERIODICITY (2)
AUTOMATED DIFFRACTION TOMOGRAPHY (2)
BENT CRYSTALS (2)
BOOK RECEIVED (2)
CBED (2)
CLUSTER MODELS (2)
COHERENT DIFFRACTIVE IMAGING (2)
COMBINATORIAL CRYSTALLOGRAPHY (2)
COMPUTATIONAL MECHANICS (2)
CORRELATION (2)
COSET SPACE (2)
CRYSTAL NETS (2)
CYLINDRICAL CRYSTALS (2)
DEBYE SCATTERING EQUATION (2)
DEFORMATION (2)
DENSITY MODIFICATION (2)
DIFFERENCE ELECTRON DENSITY (2)
DIRECT PHASING METHODS (2)
DISTORTIONS (2)
ELECTRON CRYSTALLOGRAPHY (2)
EXTINCTION (2)
FEMTOSECOND X‐RAY DIFFRACTION (2)
FLUCTUATION X‐RAY SCATTERING (2)
FORBIDDEN REFLECTIONS (2)
FULLERENES (2)
FUNDAMENTAL DOMAIN (2)
GISAXS (2)
HAADF STEM (2)
ICOSAHEDRAL RNA VIRUSES (2)
IDEAL KNOTS (2)
INTERACTION DENSITY (2)
INTERFERENCE FRINGES (2)
JOINT PROBABILITY DISTRIBUTION APPROACH (2)
JOINT PROBABILITY DISTRIBUTION FUNCTION (2)
KAOLINITE (2)
LAUE DIFFRACTION (2)
LINE GROUPS (2)
MICRODIFFRACTION (2)
MOLECULAR REPLACEMENT (2)
MONTE CARLO SIMULATION (2)
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INFONA - science communication portal

Acta Crystallographica Section A

X‐ray constrained unrestricted Hartree–Fock and Douglas–Kroll–Hess wavefunctions

A new approach to calculating powder diffraction patterns based on the Debye scattering equation

Report of the Executive Committee for 2008

Molecular crystal global phase diagrams. II. Reference lattices

Molecular crystal global phase diagrams. III. Sufficient parameter space determination

Effect of convergent beam semiangle on image intensity in HAADF STEM images

Reconstruction from a single diffraction pattern of azimuthally projected electron density of molecules aligned parallel to a single axis

The birth of the European Crystallographic Committee (ECC) and of the European Crystallographic Meetings (ECMs)

Notes for authors 2010

Nominations for the Ewald Prize

Low‐angle scattering by cylindrical structures

The long‐wavelength limit of the structure factor of amorphous silicon and vitreous silica

A neutron interferometric measurement of a phase shift induced by Laue transmission

Dense quasicrystalline tilings by squares and equilateral triangles

Analysis of time‐resolved X‐ray scattering data from solution‐state systems

Non‐equilibrium phonon dynamics studied by grazing‐incidence femtosecond X‐ray crystallography

Excited‐state molecular structures captured by X‐ray transient absorption spectroscopy: a decade and beyond

Five‐dimensional crystallography

Photoinduced structural dynamics of polar solids studied by femtosecond X‐ray diffraction

Dynamical structural science

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