Foundations of Crystallography

    

Acta Cryst. (2001). A57, 369-377  [ doi:10.1107/S0108767301000654 ]

Geometrical theory of triple junctions of CSL boundaries

V. Y. Gertsman

Synopsis: The coincidence site lattice theory of grain boundaries is extended to triple junctions. It provides a basis for analyzing triple-junction structure.

Online 21 June 2001

 

Acta Cryst. (2001). A57, 378-388  [ doi:10.1107/S0108767301001337 ]

Introduction to a general crystallography

A. Janner

Synopsis: Extended crystallographic groups, which may include hyperbolic rotations as well, are defined in terms of a faithful integral representation of a permutation group of atomic positions. This formulation unifies in a general frame the crystallographic characterization of periodic and aperiodic crystals and even of some single molecules.

Online 21 June 2001

 

Acta Cryst. (2001). A57, 389-394  [ doi:10.1107/S0108767301002343 ]

Approximate solution of the Takagi-Taupin equations for a semi-infinite crystal in the three-beam Laue-Laue case

G. Thorkildsen, H. B. Larsen and E. Weckert

Synopsis: By using the Takagi-Taupin theory, an analytical expression for the perturbation of the integrated primary diffracted power, restricted to small crystal thicknesses, is obtained. The result is found to be in perfect agreement with the full numerical solution of the fundamental equations.

Online 21 June 2001

 

Acta Cryst. (2001). A57, 395-405  [ doi:10.1107/S0108767301002434 ]

Critical examination of the radial functions in the Hansen-Coppens multipole model through topological analysis of primary and refined theoretical densities

A. Volkov and P. Coppens

Synopsis: An aspherical atom (multipole) refinement model with two sets of atomic deformation functions on each atom is tested with ab initio crystal structure factors on four different molecular crystals. The flexible model provides a quantitatively improved fit to the density and its topological parameters in the bonding regions between atoms.

Online 21 June 2001

 

Acta Cryst. (2001). A57, 406-413  [ doi:10.1107/S0108767301003087 ]

A proposal for a transition mechanism from the diamond to the lonsdaleite type

H. Sowa and E. Koch

Synopsis: A new model for the phase transformation between the diamond and the lonsdaleite type is proposed. It makes use of group-subgroup relations and describes the phase transformation as a deformation of a homogeneous sphere packing with three contacts per sphere in space group Pnna.

Online 21 June 2001

 

Acta Cryst. (2001). A57, 414-419  [ doi:10.1107/S0108767301002720 ]

The method of joint probability distribution functions applied to MAD techniques. The centric case

C. Giacovazzo and D. Siliqi

Synopsis: The joint probability distribution functions method is applied to estimate phases for MAD data.

Online 21 June 2001

 

Acta Cryst. (2001). A57, 420-428  [ doi:10.1107/S0108767300018869 ]

Phase determination and extension using X-ray multiple diffraction and the maximum-entropy method

C.-M. Wang, C.-H. Chao and S.-L. Chang

Synopsis: The extension of the phases of the structure factors of the organic crystal C₂₅H₂₅NO₂ from 77 starting individual phases derived from multiple diffraction is realized using the maximum-entropy method. More than 100 new phases are generated and an electron-density map at 1.97  Å is deduced.

Online 21 June 2001

 

Acta Cryst. (2001). A57, 429-434  [ doi:10.1107/S010876730100349X ]

Rapid neutron-diffraction data collection for hydrogen-bonding studies: application of the Laue diffractometer (LADI) to the case study zinc (tris)thiourea sulfate

J. M. Cole, G. J. McIntyre, M. S. Lehmann, D. A. A. Myles, C. Wilkinson and J. A. K. Howard

Synopsis: The successful application of the newly developed image-plate neutron Laue diffractometer, LADI, for rapid hydrogen-bonding characterization is reported. The case study concerns the non-linear optical material zinc (tris)thiourea sulfate and results from 12  h data collection compare very well with those obtained over 135  h using a crystal 13 times larger in volume and a monochromatic four-circle diffractometer at the same neutron source.

Online 21 June 2001

 

Acta Cryst. (2001). A57, 435-441  [ doi:10.1107/S0108767301004676 ]

Latent symmetry and its group theoretical determination

D. B. Litvin and V. K. Wadhawan

Synopsis: The concept of latent symmetry of a component of a composite object is defined and a method is given for its determination.

Online 21 June 2001

 

Acta Cryst. (2001). A57, 442-450  [ doi:10.1107/S0108767301004810 ]

Derivation of a scoring function for crystal structure prediction

J. Apostolakis, D. W. M. Hofmann and T. Lengauer

Synopsis: A simple learning machine is applied to the Cambridge Structural Database to derive a scoring function. The function is compared to a common force field and is successfully validated for crystal structure prediction on several hundreds of crystal structures.

Online 21 June 2001

 

Acta Cryst. (2001). A57, 451-460  [ doi:10.1107/S0108767301003397 ]

Fast differentiation algorithm and efficient calculation of the exact matrix of second derivatives

A. G. Urzhumtsev and V. Y. Lunin

Synopsis: Algorithms to calculate rapidly the exact matrix of the second derivatives of crystallographic functionals are described.

Online 21 June 2001

 

Acta Cryst. (2001). A57, 461-472  [ doi:10.1107/S0108767301003762 ]

The joint probability distributions of structure-factor doublets in displacive incommensurately modulated structures and their applicability to direct methods

R. Peschar, R. Israël and P. T. Beurskens

Synopsis: The joint probability distribution of the phase sum of two first-order satellite reflections in structures with an incommensurately displacive modulation is derived under the assumption that the phase of the associated main reflection can be calculated from the known main (or averaged) structure. The functional (dis-)similarities with conventional direct methods, employing normalized structure factors and the Cochran distribution, are assessed and test results are presented showing a significant improvement of the direct-methods phase-sum statistics when the new distribution is used.

Online 21 June 2001

 

Acta Cryst. (2001). A57, 473-474  [ doi:10.1107/S0108767301006353 ]

Inversion of dynamical electron scattering to obtain the crystal potential using data from two thicknesses

L. J. Allen, C. Koch, M. P. Oxley and J. C. H. Spence

Synopsis: A method is given to invert the multiple scattering in many-beam dynamical electron scattering to obtain the crystal potential.

Online 21 June 2001

 

Acta Cryst. (2001). A57, 475-477  [ doi:10.1107/S010876730100633X ]

The Fedorov algorithm revised

Y. L. Voytekhovsky

Synopsis: All the simple 12- to 20-hedra with no triangular and quadrilateral facets (118 in common) are calculated in the Schlegel projections.

Online 21 June 2001

 

Acta Cryst. (2001). A57, 478  [ doi:10.1107/S0108767301005980 ]

Single crystal neutron diffraction from molecular materials

Online 21 June 2001

 

Acta Cryst. (2001). A57, 478  [ doi:10.1107/S0108767301006882 ]

Worked examples in the geometry of crystals

Online 21 June 2001