Electron density study of urea using TDS-corrected X-ray diffraction data: quantitative comparison of experimental and theoretical results

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Zavodnik, Valery and Stash, Adam and Tsirelson, Vladimir and Vries de, Roelof and Feil, Dirk (1999) Electron density study of urea using TDS-corrected X-ray diffraction data: quantitative comparison of experimental and theoretical results. Acta Crystallographica Section B: Structural Science, 55 . pp. 45-54. ISSN 0108-7681

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Abstract:The electron-density distribution in urea, CO(NH2)2, was studied by high-precision single-crystal X-ray diffraction analysis at 148 (1) K. An experimental correction for TDS was applied to the X-ray intensities. Rmerge(F2) = 0.015. The displacement parameters agree quite well with results from neutron diffraction. The deformation density was obtained by refinement of 145 unique low-order reflections with the Hansen & Coppens [Acta Cryst. (1978), A34, 909-921] multipole model, resulting in R = 0.008, wR = 0.011 and S = 1.09. Orbital calculations were carried out applying different potentials to account for correlation and exchange: Hartree-Fock (HF), density-functional theory/local density approximation (DFT/LDA) and density-functional theory/generalized gradient approximation (DFT/GGA). Extensive comparisons of the deformation densities and structure factors were made between the results of the various calculations and the outcome of the refinement. The agreement between the experimental and theoretical results is excellent, judged by the deformation density and the structure factors [wR(HF) = 0.023, wR(DFT) = 0.019] and fair with respect to the results of a topological analysis. Density-functional calculations seem to yield slightly better results than Hartree-Fock calculations.
Item Type:Article
Copyright:© 1999 The International Union of Crystallography
Faculty:
Science and Technology (TNW)
Link to this item:http://purl.utwente.nl/publications/59128
Official URL:http://dx.doi.org/10.1107/S0108768198005746
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