Electron crystallography of zeolites. 3. Calcined MCM-22 and MCM-49, a case of subtle differences

2003 ◽  
Vol 218 (9) ◽  
Author(s):  
Douglas L. Dorset
Keyword(s):  
Electron Diffraction ◽  
Single Crystal ◽  
Crystal Structures ◽  
Direct Methods ◽  
Intensity Data ◽  
Electron Crystallography ◽  
Diffraction Intensity ◽  
Crystal Electron

AbstractSingle crystal electron diffraction intensity data, analyzed by direct methods for determining crystallographic phases, have been employed to seek differences between the crystal structures of calcined MCM-22 and MCM-49. A direct comparison of

Electron crystallography of zeolites. 1. Projected crystal structures of ZSM-5 and ZSM-11

2003 ◽  
Vol 218 (7) ◽  
Author(s):  
Douglas L. Dorset
Keyword(s):  
Crystal Structure ◽  
Electron Diffraction ◽  
Crystal Structures ◽  
Electron Scattering ◽  
Secondary Electron ◽  
Direct Methods ◽  
Intensity Data ◽  
Electron Crystallography ◽  
Diffraction Intensity

AbstractThe prospect of carrying out quantitative crystal structure analyses by direct methods with electron diffraction intensity data from zeolites is evaluated for two related materials: ZSM-5 and ZSM-11. The stacked plate-like arrays of ZSM-5 induce intensity perturbations from secondary electron scattering; nevertheless, the T-site positions can be found by direct methods. Intensity data from smaller ZSM-11 microcrystals are more favorable for

Electron crystallography of the polymethylene chain. 3. Three-dimensional crystal structure of a refined paraffin wax1

1999 ◽  
Vol 214 (6) ◽  
Author(s):  
D. L. Dorset
Keyword(s):  
Crystal Structure ◽  
Electron Diffraction ◽  
Three Dimensional ◽  
Intensity Data ◽  
Electron Crystallography ◽  
Diffraction Intensity ◽  
Orthorhombic Space Group ◽  
Oriented Samples ◽  
Commercial Paraffin Wax ◽  
Dimensional Crystal

AbstractThe three-dimensional crystal structure of a commercial paraffin wax has been determined from electron diffraction intensity data collected from epitaxially oriented samples. The orthorhombic space group is

Electron crystallography of membrane phospholipids

1992 ◽  
Vol 50 (1) ◽  
pp. 430-431
Author(s):  
Douglas L. Dorset
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Crystal Structure Analysis ◽  
Subsequent Paper ◽  
Intensity Data ◽  
Membrane Phospholipids ◽  
Electron Crystallography ◽  
X Ray ◽  
Diffraction Patterns ◽  
Crystal Electron

Membrane phospholipids are notoriously difficult to crystallize to sample sizes suitable for collection of single crystal X-ray intensity data, accounting for the relatively few crystal structures which have been reported to date. At the 24th Annual EMSA meeting, Parsons and Nyburg suggested that the enhanced scattering of electrons by matter be exploited to obtain single crystal electron diffraction patterns from the more readily available microcrystalline preparations, an example of which was shown in a subsequent paper. For almost 20 years ve have investigated the utility of such intensity data for ab initio crystal structure analysis.

Serial electron crystallography: merging diffraction data through rank aggregation

2017 ◽  
Vol 50 (3) ◽  
pp. 885-892 ◽  
Author(s):  
Stef Smeets ◽  
Wei Wan
Keyword(s):  
Electron Diffraction ◽  
Diffraction Data ◽  
Precise Measurement ◽  
Simulated Data ◽  
Direct Methods ◽  
Rank Aggregation ◽  
Polycrystalline Materials ◽  
Electron Crystallography ◽  
Diffraction Intensity ◽  
Dynamical Nature

Serial electron crystallography is being developed as an alternative way to collect diffraction data on beam-sensitive polycrystalline materials. Merging serial diffraction data from a large number of snapshots is difficult, and the dynamical nature of electron diffraction prevents the use of existing methods that rely on precise measurement of kinematical reflection intensities. To overcome this problem, an alternative method that uses rank aggregation to combine the rankings of relative reflection intensities from a large number of snapshots has been developed. The method does not attempt to accurately model the diffraction intensity, but instead optimizes the most likely ranking of reflections. As a consequence, the problem of scaling individual snapshots is avoided entirely, and requirements for the data quality and precision are low. The method works best when reflections can be fully measured, but the benefit over measuring partial intensities is small. Since there were no experimental data available for testing rank-based merging, the validity of the approach was assessed through a series of simulated serial electron diffraction datasets with different numbers of frames and varying degrees of errors. Several programs have been used to show that these rank-merged simulated data are good enough forab initiostructure determination using several direct methods programs.

scholarly journals Structure determination from X-ray powder diffraction data at low resolution

2014 ◽  
Vol 70 (a1) ◽  
pp. C143-C143
Author(s):  
Hongliang Xu
Keyword(s):  
Single Crystal ◽  
Diffraction Pattern ◽  
Crystal Structures ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Structure Determination ◽  
Direct Methods ◽  
Atomic Resolution ◽  
Powder Diffraction Data ◽  
Low Resolution

Knowledge of the structural arrangement of atoms in solids is necessary to facilitate the study of their properties. The best and most detailed structural information is obtained when the diffraction pattern of a single crystal a few tenths of a millimeter in each dimension is analyzed, but growing high-quality crystals of this size is often difficult, sometimes impossible. However, many crystallization experiments that do not yield single crystals do yield showers of randomly oriented micro-crystals that can be exposed to X-rays simultaneously to produce a powder diffraction pattern. Direct Methods routinely solve crystal structures when single-crystal diffraction data are available at atomic resolution (1.0-1.2Å), but fail to determine micro-crystal structures due to reflections overlapping and low-resolution powder diffraction data. By artificially and intelligently extending the measured data to atomic resolution, we have successfully solved structures having low-resolution diffraction data that were hard to solve by other direct-method based computation procedures. The newly developed method, Powder Shake-and-Bake, is implemented in a computer program PowSnB. PowSnB can be incorporated into the state-of-the-art software package EXPO that includes powder data reduction, structure determination and structure refinement. The new combination could have potential to solve structures that have never been solved before by direct-methods approach.

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