scholarly journals Structure determination of organic compounds by a fit to the pair distribution function from scratch without prior indexing

2021 ◽  
Vol 54 (3) ◽  
Author(s):  
Carina Schlesinger ◽  
Stefan Habermehl ◽  
Dragica Prill

A method for the ab initio crystal structure determination of organic compounds by a fit to the pair distribution function (PDF), without prior knowledge of lattice parameters and space group, has been developed. The method is called `PDF-Global-Fit' and is implemented by extension of the program FIDEL (fit with deviating lattice parameters). The structure solution is based on a global optimization approach starting from random structural models in selected space groups. No prior indexing of the powder data is needed. The new method requires only the molecular geometry and a carefully determined PDF. The generated random structures are compared with the experimental PDF and ranked by a similarity measure based on cross-correlation functions. The most promising structure candidates are fitted to the experimental PDF data using a restricted simulated annealing structure solution approach within the program TOPAS, followed by a structure refinement against the PDF to identify the correct crystal structure. With the PDF-Global-Fit it is possible to determine the local structure of crystalline and disordered organic materials, as well as to determine the local structure of unindexable powder patterns, such as nanocrystalline samples, by a fit to the PDF. The success of the method is demonstrated using barbituric acid as an example. The crystal structure of barbituric acid form IV solved and refined by the PDF-Global-Fit is in excellent agreement with the published crystal structure data.

Author(s):  
P. Ballirano ◽  
R. Caminiti ◽  
C. Sadun ◽  
V. M. Coiro ◽  
G. Mancini ◽  
...  

AbstractThe structures of cetylpyridiniumammonium bromide (CPyB) and cetylquinuclidinium bromide (CQB), two tetraalkylammonium bromide surfactants, are reported. In particular, whereas the structure solution of CPyB was carried out through conventional single-crystal diffractometry, the structure of CQB has been determined by means of powder diffractometry. CPyB crystallizes in


2015 ◽  
Vol 71 (a1) ◽  
pp. s383-s384
Author(s):  
Dominik Schaniel ◽  
El-Eulmi Bendeif ◽  
Axel Gansmuller ◽  
Kuan-Ying Hsieh ◽  
Sebastien Pillet ◽  
...  

1994 ◽  
Vol 376 ◽  
Author(s):  
S. J. L. Billinge ◽  
G. H. Kwei

ABSTRACTWe describe the use of neutron powder diffraction for studying the local structure of high-temperature superconductors. This is accomplished by carrying out a pair distribution function (PDF) analysis. This approach does not presume a periodic structure and allows short range deviations from perfect crystalline order to be observed. Data from a sample of La2CuO4 collected on two different diffractometers are compared to determine the degree of reproducibility of the results. It is found that the data reproduce very well; however, a model-PDF, fit to the data assuming the average crystal structure in the low-temperature-orthorhombic (LTO) phase, differs from the data in a number of significant ways. This is related to earlier observations that the local structure of the La1.875Ba0.125CuO4 compound differs from the average crystal structure.


2006 ◽  
Vol 18 (1) ◽  
pp. 100-106 ◽  
Author(s):  
Gianluca Paglia ◽  
Emil S. Božin ◽  
Damjan Vengust ◽  
Dragan Mihailovic ◽  
Simon J. L. Billinge

Author(s):  
Th. Proffen ◽  
S. J. L. Billinge ◽  
T. Egami ◽  
D. Louca

AbstractModern materials and their properties are often characterized by varying degrees of disorder. Routine crystallographic structure solution only reveals the average structure. The study of Bragg and diffuse scattering yields the local atomic arrangements holding the key to understanding increasingly complex materials. In this paper we review the pair distribution function technique used to unravel the local structure. We aim to give a practical overview and make this method easily accessible to the wider scientific community.


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