Direct methods and simulated annealing: a hybrid approach for powder diffraction data

The solution of crystal structures from powder data using direct methods can be very difficult if the quality of the diffraction pattern is low and if no heavy atoms are present in the molecule. On the contrary, the use of direct‐space methods does not require good quality diffraction data, but if a...

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Bibliographic Details
Published in:Journal of applied crystallography 2008-02, Vol.41 (1), p.56-61
Main Authors: Altomare, Angela, Caliandro, Rocco, Cuocci, Corrado, Giacovazzo, Carmelo, Moliterni, Anna Grazia Giuseppina, Rizzi, Rosanna, Platteau, Cyril
Format: Article
Language:English
Subjects:
Algorithms
Crystal structure
Crystallography
Diffraction
direct methods
Monte Carlo method
Monte Carlo simulation
Research methodology
simulated annealing
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Summary:The solution of crystal structures from powder data using direct methods can be very difficult if the quality of the diffraction pattern is low and if no heavy atoms are present in the molecule. On the contrary, the use of direct‐space methods does not require good quality diffraction data, but if a molecular model is available, the structure solution is limited principally by the number of degrees of freedom used to describe the model. The combination of the information contained in the electron density map (direct methods) with the Monte Carlo method, which uses simulated annealing as a global minimization algorithm (direct‐space techniques), can be a useful tool for crystal structure solution, especially for organic structures. A modified and improved version of this approach [Altomare et al. (2003), J. Appl. Cryst.36, 230–238] has been implemented in the EXPO2004 program and is described here.
ISSN:1600-5767
0021-8898
1600-5767
DOI:10.1107/S0021889807054192