Electron density-functional theory and x-ray structure factors

1987 ◽  
Vol 35 (15) ◽  
pp. 7887-7890 ◽  
Author(s):  
Mel Levy ◽  
Jerome A. Goldstein
Keyword(s):  
Density Functional Theory ◽  
Electron Density ◽  
Density Functional ◽  
Functional Theory ◽  
X Ray ◽  
Electron Density Functional Theory ◽  
Structure Factors

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

1999 ◽  
Vol 55 (1) ◽  
pp. 45-54 ◽  
Author(s):  
Valery Zavodnik ◽  
Adam Stash ◽  
Vladimir Tsirelson ◽  
Roelof de Vries ◽  
Dirk Feil
Keyword(s):  
Density Functional Theory ◽  
Electron Density ◽  
Density Functional ◽  
X Ray Diffraction ◽  
Functional Theory ◽  
X Ray ◽  
Hartree Fock ◽  
Deformation Density ◽  
Structure Factors ◽  
Theoretical Results

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. R merge(F 2) = 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.

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