Structure solution of a novel aluminium methylphosphonate using a new simulated annealing program and powder X-ray diffraction data

2002 ◽  
pp. 808-809 ◽  
Author(s):  
Mark Edgar ◽  
Vinton J. Carter ◽  
David P. Tunstall ◽  
Paramjit Grewal ◽  
Vincent Favre-Nicolin ◽  
...  
Keyword(s):  
Simulated Annealing ◽  
Diffraction Data ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structure Solution

In situ structure solution of helical sulphur at 3GPa and 400ºC

2001 ◽  
Vol 216 (8) ◽  
Author(s):  
W. A. Crichton ◽  
G. B. M. Vaughan ◽  
M. Mezouar
Keyword(s):  
Global Optimization ◽  
Simulated Annealing ◽  
Rietveld Refinement ◽  
Diffraction Data ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Structure Solution

AbstractThe structure of a 2-chain helical form of sulphur with 9 atoms per unit-cell has been determined from powder synchrotron x-ray diffraction data obtained at 3 GPa and 400ºC, using a combination of global optimization, simulated annealing and Rietveld refinement techniques. Final refinement of the structure in trigonal space group

Advantages of a Redefinition of Variable-Space in Direct-Space Structure Solution from Powder X-Ray Diffraction Data

ChemPhysChem ◽  
2007 ◽  
Vol 8 (5) ◽  
pp. 650-653 ◽  
Author(s):  
Zhongfu Zhou ◽  
Veronique Siegler ◽  
Eugene Y. Cheung ◽  
Scott Habershon ◽  
Kenneth D. M. Harris ◽  
...  
Keyword(s):  
Diffraction Data ◽  
Space Structure ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structure Solution ◽  
Variable Space

Unraveling the Structure of Decagonal Approximants by “Brute Force” Deconvolution of the Experimental Autocorrelation Function

2000 ◽  
Vol 643 ◽  
Author(s):  
Michael A. Estermann ◽  
Katja Lemster ◽  
Walter Steurer
Keyword(s):  
Autocorrelation Function ◽  
Diffraction Data ◽  
Brute Force ◽  
X Ray Diffraction ◽  
Large Unit ◽  
X Ray ◽  
Structure Building ◽  
Lack Of Information ◽  
Structure Solution ◽  
Unit Cells

AbstractMethods for the ab initio structure analysis of periodic approximant phases from single- crystal X-ray diffraction data are presented. These methods are particularly suited to complex approximant structures with large unit cells and strong pseudosymmetry (where routine X-ray structure solution tools fail) and are based on the “brute-force” deconvolution of the experimentally measured autocorrelation function. This function is obtained directly by a simple Fourier transform of the measured X-ray diffraction intensities. Sub-optimal diffraction data from twinned, nanodomain and polycrystalline specimens can be processed despite the inevitable lack of information due to reflection overlap and limited resolution. The deconvolution process allows complex approximant structures to be unraveled without prior knowledge about the structure-building motifs. Examples are presented for the systems Al-Co-Ni and Al-Co-(Ta).

Temperature phase changes in solid bicyclo[3.3.1]nonane-2,6-dione and bicyclo[3.3.1]nonane-3,7-dione from powder X-ray diffraction data

2007 ◽  
Vol 40 (4) ◽  
pp. 702-709 ◽  
Author(s):  
Michela Brunelli ◽  
Marcus A. Neumann ◽  
Andrew N. Fitch ◽  
Asiloé J. Mora
Keyword(s):  
Simulated Annealing ◽  
Crystal Structures ◽  
Phase Ii ◽  
Diffraction Data ◽  
Direct Methods ◽  
Temperature Phase ◽  
Molecular Orbital Calculations ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray

The crystal structures of bicyclo[3.3.1]nonane-2,6-dione and bicyclo[3.3.1]nonane-3,7-dione have been solved by direct methods and by direct-space simulated annealing, respectively, from powder synchrotron X-ray diffraction data. Both compounds have a transition to a face-centred-cubic orientationally disordered phase (phase I) near 363 K, as shown by differential scanning calorimetry and powder diffraction measurements. Phase II of bicyclo[3.3.1]nonane-2,6-dione, which occurs below 363 K, is monoclinic, space groupC2/c, witha= 7.38042 (4),b= 10.38220 (5),c= 9.75092 (5) Å and β = 95.359 (1)° at 80 K. Phase II of bicyclo[3.3.1]nonane-3,7-dione, which occurs below 365 K, is tetragonal, space groupP41212, witha= 6.8558 (1) andc= 16.9375 (1) Å at 100 K. This phase coexists in a biphasic mixture with a minor monoclinic phase II′ [a= 11.450 (6),b = 20.583 (1),c= 6.3779 (3) Å, β = 94.7555 (5)°, at 100 K] detected in the sample, which impeded indexing with standard programs. The crystal structures of phases II were solved by direct methods and by direct-space simulated annealing, employing powder synchrotron X-ray diffraction data of increased instrumental intensity and resolution from the ID31 beamline at the ESRF, and novel indexing algorithms.Ab initiomolecular orbital calculations on the two systems are reported. In the solid state, the molecules pack in chair–chair conformation; molecular structures and packing are discussed.

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