Foundations of Crystallography

 

Acta Cryst. (2001). A57, 629-641  [ doi:10.1107/S0108767301008509 ]

Systematic intensity errors caused by spectral truncation: origin and remedy

A. T. H. Lenstra, J. F. J. Van Loock, B. Rousseau and S. T. Maes

Synopsis: X-ray absorption by the monochromator determines the wavelength dispersion in the monochromated X-ray beam and explains the values of 0.03, 0.14 and 0.16 for graphite(002)-monochromated Cu, Mo and Rh radiation. To eliminate the systematic intensity truncation errors, caused by the large wavelength dispersion, a correction is proposed based on the applied scan angle and the real beam spectrum.

Online 26 October 2001

 

Acta Cryst. (2001). A57, 642-648  [ doi:10.1107/S010876730100890X ]

Chirality-induced `forbidden' reflections in X-ray resonant scattering

V. E. Dmitrienko and E. N. Ovchinnikova

Synopsis: It is shown that additional Bragg reflections can appear in resonant near-edge X-ray diffraction exclusively owing to the local chirality associated with the left-right asymmetric environment of scattering atoms. This effect occurs even in centrosymmetric crystals, which are not gyrotropic in optics, and some realistic examples are considered in detail (-Fe₂O₃, LiNbO₃ etc.).

Online 26 October 2001

 

Acta Cryst. (2001). A57, 649-655  [ doi:10.1107/S0108767301009102 ]

Coincidence site lattice theory of multicrystalline ensembles

V. Y. Gertsman

Synopsis: The coincidence site lattice theory is extended to multicrystalline ensembles, such as quadruple points and multiple junctions of grains.

Online 26 October 2001

 

Acta Cryst. (2001). A57, 656-662  [ doi:10.1107/S0108767301010182 ]

Relativistic analytical wave functions and scattering factors for neutral atoms beyond Kr and for all chemically important ions up to I^-

P. Macchi and P. Coppens

Synopsis: Relativistic wave functions for elements with Z  =  37-54 have been fitted with a linear combination of Slater-type functions for use in charge-density analysis. Numerical relativistic wave functions have been calculated for all chemically relevant ions up to Z  =  54, and corresponding analytical espressions have been derived. The calculated X-ray scattering factors are parameterized with six Gausian functions. Results are available at http://harker.chem.buffalo.edu.

Online 26 October 2001

 

Acta Cryst. (2001). A57, 663-677  [ doi:10.1107/S0108767301010698 ]

Electron-density distribution in stishovite, SiO₂: a new high-energy synchrotron-radiation study

A. Kirfel, H.-G. Krane, P. Blaha, K. Schwarz and T. Lippmann

Synopsis: 100  keV synchrotron radiation was used to obtain essentially absorption- and extinction-free data for the refinement of a multipole model electron-density distribution and ensuing topological analysis. Results are compared with ab initio density functional theory calculations and correlated with Si-O bond properties from geometry-optimized hydroxyacid molecules.

Online 26 October 2001

 

Acta Cryst. (2001). A57, 678-680  [ doi:10.1107/S0108767301010650 ]

A simple inverse method for calculating electron-density maps

J. R. Somoza, A. Szöke and H. Szöke

Synopsis: This paper describes a real-space reconstruction method for calculating electron-density maps.

Online 26 October 2001

 

Acta Cryst. (2001). A57, 681-685  [ doi:10.1107/S0108767301009187 ]

A fast Newton method for entropy maximization in statistical phase estimation

Z. Wu, G. N. Phillips, R. Tapia and Y. Zhang

Synopsis: A fast Newton method is developed to solve the entropy maximization problem in the Bayesian statistical approach to phase estimation. The method requires only O(n  log  n) instead of standard O(n³) floating point operations per iteration, while converging in the same rate as the standard Newton method.

Online 26 October 2001

 

Acta Cryst. (2001). A57, 686-689  [ doi:10.1107/S0108767301012697 ]

Is the border surface of a crystal indeed the weakest point of the dynamical theory of diffraction?

P. Dub and O. Litzman

Synopsis: In Laue's dynamical theory of diffraction, the boundary conditions claim to introduce a mathematical plane instead of the discrete atomic surface of the crystal. This assumption is analyzed from the point of view of Ewald's theory based on the microscopic discrete model of a crystal, where no boundary conditions are needed.

Online 26 October 2001

 

Acta Cryst. (2001). A57, 690-699  [ doi:10.1107/S0108767301013186 ]

A new phasing method based on the principle of minimum charge

P. Kalugin

Synopsis: A description of a new phasing method and demonstration of its use for crystal and quasicrystal structure determination are presented.

Online 26 October 2001

 

Acta Cryst. (2001). A57, 700-707  [ doi:10.1107/S0108767301011837 ]

The method of joint probability distribution functions applied to MAD techniques. The two-wavelength case for acentric crystals

C. Giacovazzo and D. Siliqi

Synopsis: The joint probability distribution functions method is applied to estimate phases from multiple-wavelength anomalous dispersion (MAD) data in the two-wavelength case for acentric crystals.

Online 26 October 2001

 

Acta Cryst. (2001). A57, 708-712  [ doi:10.1107/S0108767301014064 ]

Ultra-high-angle double-crystal X-ray diffractometry (U-HADOX) for determining a change in the lattice spacing: theory

A. Okazaki and Y. Soejima

Synopsis: Extension of Bragg angle up to has been examined theoretically for high-angle double-crystal X-ray diffractometry (HADOX). It is shown that an accuracy of a change in the lattice spacing to one part in can be attained.

Online 26 October 2001

 

Acta Cryst. (2001). A57, 713-728  [ doi:10.1107/S0108767301012582 ]

Atomic scattering factors for K-shell electron energy-loss spectroscopy

M. P. Oxley and L. J. Allen

Synopsis: Atomic scattering factors for -shell electron energy-loss spectroscopy have been calculated for elements in the range = 6 (carbon) to = 50 (tin).

Online 26 October 2001

 

Acta Cryst. (2001). A57, 729-730  [ doi:10.1107/S0108767301006547 ]

Magnetic space-group types

D. B. Litvin

Synopsis: Opechowski-Guccione symbols for the 1651 magnetic space-group types are uniquely specified independent of International Tables for Crystallography.

Online 26 October 2001

 

Acta Cryst. (2001). A57, 731-732  [ doi:10.1107/S0108767301010212 ]

Symmetry relations of magnetic twin laws

J. Schlessman and D. B. Litvin

Synopsis: Magnetic symmetry groups and magnetic twinning groups of domain pairs are tabulated.

Online 26 October 2001

 

Acta Cryst. (2001). A57, 733-735  [ doi:10.1107/S0108767301010807 ]

A modified X  -  Y method

Y. Chen and W.-P. Su

Synopsis: To solve the crystallographic phase problem, simulated annealing is used to minimize a total cost function with respect to atomic coordinates. The total cost function consists of the X  -  Y function plus a crystallographic residual.

Online 26 October 2001

 

Acta Cryst. (2001). A57, 736-738  [ doi:10.1107/S0108767301012363 ]

C₂₀ to C₆₀ fullerenes: combinatorial types and symmetries

Y. L. Voytekhovsky and D. G. Stepenshchikov

Synopsis: A figure giving the point groups for all combinatorially non-isomorphic C₂₀ to C₆₀ fullerenes (5770 in common) is contributed. The fullerenes of 6 to 120 automorphism group orders (80 in common) are drawn in the Shlegel projections and characterized by the point groups.

Online 26 October 2001

 

Acta Cryst. (2001). A57, 739-740  [ doi:10.1107/S0108767301012624 ]

An efficient ab initio calculation of powder diffraction intensity using Debye's equation

R. F. Grover and D. R. McKenzie

Synopsis: A new efficient algorithm is presented for the evaluation of the Debye equation for powder diffraction intensity having applications for achieving direct intensity profile fitting.

Online 26 October 2001

 

Acta Cryst. (2001). A57, 741-795  [ doi:10.1107/S0108767301015495 ]

International Union of Crystallography Eighteenth General Assembly and International Congress of Crystallography Glasgow, UK, 4-13 August 1999

Online 26 October 2001

 

Acta Cryst. (2001). A57, 796-797  [ doi:10.1107/S0108767301016567 ]

Prices of IUCr journals

Online 26 October 2001