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Bridging the gap – structure determination of the red polymorph of tetrahexylsexithiophene by Monte Carlo simulated annealing, first‐principles DFT calculations and Rietveld refinement
Author(s) -
Neumann Marcus A.,
Tedesco Consiglia,
Destri Silvia,
Ferro Dino R.,
Porzio William
Publication year - 2002
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/s0021889802002844
Subject(s) - rietveld refinement , crystallography , simulated annealing , monte carlo method , density functional theory , crystal structure , powder diffraction , diffraction , materials science , lattice energy , chemistry , computational chemistry , physics , mathematics , algorithm , quantum mechanics , statistics
The crystal structure of the red polymorph of tetrahexylsexithiophene (THST) is solved from X‐ray powder diffraction data by a direct‐space Monte Carlo simulated‐annealing approach. First‐principles density functional theory (DFT) calculations are used to distinguish between three nearly identical solutions in the space groups C 2/ m , C 2 and P and to improve the overall accuracy of the crystal structure. The correct space group is found to be C 2/ m . In all space groups, the thiophene backbone is planar and the hexyl side chains assume an all‐ trans conformation except for two terminal methyl residues, which adopt a gauche orientation. The ability of first‐principles DFT calculations to provide atomic coordinates of single‐crystal quality is demonstrated by lattice‐energy minimization of the known crystal structure of the yellow polymorph of THST. The combination of Monte Carlo simulated annealing, first‐principles DFT calculations and Rietveld refinement presented in this paper is generally applicable. It provides a powerful alternative to standard approaches in cases where the information content of the powder diffraction pattern alone is insufficient to distinguish between different structure solutions. DFT calculations can also provide invaluable guidance in Rietveld refinement.