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Solution of organic crystal structures from powder diffraction by combining simulated annealing and direct methods
Author(s) -
Altomare Angela,
Caliandro Rocco,
Giacovazzo Carmelo,
Moliterni Anna Grazia Giuseppina,
Rizzi Rosanna
Publication year - 2003
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889802022641
Subject(s) - simulated annealing , monte carlo method , powder diffraction , ab initio , diffraction , direct methods , electron density , annealing (glass) , crystal structure , experimental data , minification , crystal (programming language) , materials science , chemistry , statistical physics , computational physics , crystallography , molecular physics , algorithm , electron , computer science , physics , optics , mathematics , organic chemistry , quantum mechanics , statistics , composite material , programming language
The ab initio crystal structure solution from powder diffraction data can be attempted via direct methods. If heavy atoms are present, they are usually correctly located; then some crystal chemical information can be exploited to complete the partial structure model. Organic structures are more resistant to direct methods; as an alternative, their molecular geometry is used as prior information for Monte Carlo methods. In this paper, a new procedure is described which combines the information contained in the electron density map provided by direct methods with a Monte Carlo method which uses simulated annealing as a minimization algorithm. A figure of merit has been designed based on the agreement between the experimental and calculated profiles, and on the positions of the peaks in the electron density map. The procedure is completely automatic and has been included in EXPO ; its performance has been validated and tested for a set of known molecular structures.