Foundations of Crystallography

 

Acta Cryst. (1999). A55, 783-789  [ doi:10.1107/S0108767399000197 ]

Reverse Monte Carlo modelling of neutron powder diffraction data

A. Mellergård and R. L. McGreevy

Synopsis: A new reverse Monte Carlo (RMC) method for modelling both lattice and magnetic disorder in powder crystalline materials is presented.

Online September 1999

 

Acta Cryst. (1999). A55, 790-802  [ doi:10.1107/S0108767399001002 ]

Chirality and general aspects of symmetry

B. B. Smirnov, O. V. Lebedev and A. V. Evtushenko

Synopsis: Rigorous and universal rules for qualitative and quantitative estimation of chirality have been developed.

Online September 1999

 

Acta Cryst. (1999). A55, 803-810  [ doi:10.1107/S0108767399001610 ]

Structure of the alloy Ti₅₀Ni_48.7Co_1.3

Z. Lekston, V. E. Naish, T. V. Novoselova and I. V. Sagaradze

Synopsis: The structure of the R phase of the alloy Ti₅₀Ni_48.7Co_1.3 was determined by the crystallogeometric analysis of martensitic transformations in titanium nickelide. This analysis is based on the concept of cooperative thermal vibrations of the (110)-like planes in the b.c.c. and B2 structures and their freezing (transformation to static displacements) at the point of the phase transition.

Online September 1999

 

Acta Cryst. (1999). A55, 811-820  [ doi:10.1107/S0108767399001622 ]

Structure characterization and predictability by Voronoi analysis

S. W. Christensen and N. W. Thomas

Synopsis: It is demonstrated how to extract information on the structure-forming properties of atoms through the analysis of atomic structures via the Voronoi tessellation.

Online September 1999

 

Acta Cryst. (1999). A55, 821-827  [ doi:10.1107/S0108767399001993 ]

Electron-density-based calculations of intermolecular energy: case of urea

K. Yu. Suponitsky, V. G. Tsirelson and D. Feil

Synopsis: Calculation of the interaction energy of urea from the experimental and Hartree-Fock X-ray structure amplitudes has been performed using a modified atom-atom approximation. Similar electron-density distributions yield widely different atomic multipole moments, resulting in unphysical energy differences.

Online September 1999

 

Acta Cryst. (1999). A55, 828-839  [ doi:10.1107/S0108767399002068 ]

The phase transitions and crystal structures of Ba₃RM₂O_7.5 complex oxides (R = rare-earth elements, M = Al, Ga)

A. M. Abakumov, R. V. Shpanchenko, O. I. Lebedev, G. Van Tendeloo, S. Amelinckx and E. V. Antipov

Synopsis: The structures of -Ba₃RAl₂O_7.5 and -Ba₃RM₂O_7.5 (R = rare-earth elements, M = Al, Ga) complex oxides have been studied by X-ray diffraction, electron diffraction and high-resolution electron microscopy. The order-disorder phase transition between the orthorhombic high-temperature form and the monoclinic low-temperature form results from sequential migration of oxygen atoms along the strings of vertex-sharing tetrahedral Al₂O₇ pairs.

Online September 1999

 

Acta Cryst. (1999). A55, 840-854  [ doi:10.1107/S0108767399002986 ]

X-ray diffraction in perfect t  ×  l crystals. Rocking curves

G. Thorkildsen and H. B. Larsen

Synopsis: The theory for rocking curves in perfect rectangular crystals is outlined using the Takagi-Taupin equations. Calculated examples are presented for different scattering geometries in germanium and silicon.

Online September 1999

 

Acta Cryst. (1999). A55, 855-863  [ doi:10.1107/S010876739900313X ]

Diffraction of 100 to 200  keV X-rays from an Si_1-xGe_x gradient crystal: comparison with results from dynamical theory

S. Keitel, C. Malgrange, T. Niemöller and J. R. Schneider

Synopsis: A large Si_1-xGe_x gradient crystal was investigated by means of high-energy synchrotron radiation in the energy range 100-200  keV. The experimental data are explained by geometrical optics theory.

Online September 1999

 

Acta Cryst. (1999). A55, 864-870  [ doi:10.1107/S0108767399003219 ]

Wavelength-modulated diffraction: a new method for phase determination

H. Iwasaki, T. Yurugi and Y. Yoshimura

Synopsis: A new method has been developed in which the intensity of Bragg reflections is measured while changing continually the radiation wavelength over a range in the vicinity of the absorption edge. The intensity gradient with respect to the wavelength is in a simple relation to the real and imaginary parts of the structure factor and its phase can be derived by solving two simultaneous linear equations.

Online September 1999

 

Acta Cryst. (1999). A55, 871-883  [ doi:10.1107/S010876739900330X ]

Reduced projection operators and algebraic expressions for the symmetry-adapted functions of the icosahedral group

P.-D. Fan, J.-Q. Chen and J. P. Draayer

Synopsis: Algebraic expressions for the reduced projection operators for the irreducible representation of the icosahedral group are found by using the double-induced technique and eigenfunction method.

Online September 1999

 

Acta Cryst. (1999). A55, 884-890  [ doi:10.1107/S0108767399003499 ]

Tensor distinction of domain pairs in ferroic crystals

D. B. Litvin

Synopsis: Domain pairs arising in ferroic transitions are classified. Physical property tensors are tabulated according to their ability to distinguish between domains of each class of domain pairs.

Online September 1999

 

Acta Cryst. (1999). A55, 891-900  [ doi:10.1107/S0108767399003918 ]

Exponential Shake-and-Bake: theoretical basis and applications

H. A. Hauptman, H. Xu, C. M. Weeks and R. Miller

Synopsis: The cosine minimal function used in Shake-and-Bake has been replaced by a function of exponential type. With proper choice of parameter values, the exponential function yielded significantly higher success rates for several P1 structures.

Online September 1999

 

Acta Cryst. (1999). A55, 901-907  [ doi:10.1107/S0108767399004250 ]

Dynamical scattering and electron diffraction from thin polymer lamellar crystals - poly(tert-butylethylene sulfide)

D. L. Dorset, P. Dumas, L. Cartier and B. Lotz

Synopsis: The breakdown of Friedel's law in electron diffraction patterns from a polar polymer structure is readily explained by multiple-beam dynamical scattering calculations. While not restricting an ab initio structure analysis, the Bijvoet differences can provide additional structural information.

Online September 1999

 

Acta Cryst. (1999). A55, 908-915  [ doi:10.1107/S0108767399004262 ]

Absolute structure and absolute configuration

H. D. Flack and G. Bernardinelli

Synopsis: The fundamental notions associated with the determination and reporting of absolute structure and absolute configuration from crystal structure analysis are treated in detail.

Online September 1999

 

Acta Cryst. (1999). A55, 916-925  [ doi:10.1107/S0108767399005000 ]

Seminvariant density decomposition and connectivity analysis and their application to very low resolution macromolecular phasing

V. Y. Lunin, N. L. Lunina and A. G. Urzhumtsev

Synopsis: The suggested procedure of Fourier-series decomposition provides a new tool for analysis of low-resolution macromolecular images. Together with the suggested connectivity-based criterion, the decomposition allows a search for the macromolecular position in a crystal by phasing several very low resolution reflections.

Online September 1999

 

Acta Cryst. (1999). A55, 926-932  [ doi:10.1107/S0108767399005176 ]

Parameterization of the temperature dependence of the Debye-Waller factors

H. X. Gao and L.-M. Peng

Synopsis: Parameterization has been made for the temperature dependence of the Debye-Waller factors of 68 elemental crystals and 17 compounds with the zinc-blende structure.

Online September 1999

 

Acta Cryst. (1999). A55, 933-938  [ doi:10.1107/S0108767399005188 ]

Quantitative phase determination for macromolecular crystals using stereoscopic multibeam imaging

S.-L. Chang, C.-H. Chao, Y.-S. Huang, Y.-C. Jean, H.-S. Sheu, F.-J. Liang, H.-C. Chien, C.-K. Chen and H. S. Yuan

Synopsis: Without invoking anomalous dispersion and heavy-atom derivatives, it is demonstrated that it is possible to directly determine the phases of a large number of reflections collected in a short time from macromolecular crystals using a stereoscopic oscillation-crystal imaging technique in a multibeam diffraction geometry.

Online September 1999

 

Acta Cryst. (1999). A55, 939-954  [ doi:10.1107/S0108767399005401 ]

Refinement of crystal structural parameters using two-dimensional energy-filtered CBED patterns

K. Tsuda and M. Tanaka

Synopsis: A new method to refine crystal structural parameters using energy-filtered convergent-beam electron diffraction (CBED), which is applicable to nanometre-size crystal structure analysis, is proposed.

Online September 1999

 

Acta Cryst. (1999). A55, 955-962  [ doi:10.1107/S0108767399007138 ]

Tunable X-ray polarization reflector with perfect crystals

Y. Hasegawa, Y. Ueji, K. Okitsu, J. M. Ablett, D. P. Siddons and Y. Amemiya

Synopsis: A transmission-type X-ray polarizer is realised with a thin Bragg reflector as a polarizing filter. This device gave a polarization ratio, defined as , higher than 10⁵.

Online September 1999

 

Acta Cryst. (1999). A55, 963-964  [ doi:10.1107/S0108767399003487 ]

Magnetic subperiodic groups

D. B. Litvin

Synopsis: The magnetic subperiodic groups are defined and given symbols based on the symbols of non-magnetic subperiodic groups in Volume E of International Tables for Crystallography.

Online September 1999

 

Acta Cryst. (1999). A55, 965-967  [ doi:10.1107/S0108767399009733 ]

On the errors in molecular dipole moments derived from accurate diffraction data

P. Coppens, A. Volkov, Y. Abramov and T. Koritsanszky

Synopsis: The origin dependence of the errors in an X-ray molecular dipole moment is discussed and a suitable choice of origin is defined.

Online September 1999

 

Acta Cryst. (1999). A55, 968-972  [ doi:10.1107/S0108767399005942 ]

On reflection

Online September 1999

 

Acta Cryst. (1999). A55, 972-973  [ doi:10.1107/S0108767399007333 ]

Physical properties of quasicrystals

Online September 1999

 

Acta Cryst. (1999). A55, 973  [ doi:10.1107/S0108767399001889 ]

Crystallography

Online September 1999

 

Acta Cryst. (1999). A55, 973  [ doi:10.1107/S0108767399001567 ]

Ultrafast dynamics of quantum systems. Physical processes and spectroscopic techniques

Online September 1999

 

Acta Cryst. (1999). A55, 973  [ doi:10.1107/S0108767399004791 ]

Einfuehrung in die kristallographie

Online September 1999

 

Acta Cryst. (1999). A55, 973  [ doi:10.1107/S0108767399001555 ]

Crystallography across the sciences

Online September 1999