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Related Experiment Videos

Extracting charge density distributions from diffraction data: a model study on urea

de Vries RY1, Feil, Tsirelson

  • 1Chemical Physics Laboratory, University of Twente, Enschede, The Netherlands.

Acta Crystallographica. Section B, Structural Science
|March 29, 2000
PubMed
Summary

Extracting electron density distributions (EDD) using multipole refinement is unreliable for non-centrosymmetric crystals. Adding experimental errors significantly deforms the interaction density, making accurate EDD extraction impossible from X-ray diffraction data.

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Area of Science:

  • Crystallography
  • Materials Science
  • Computational Chemistry

Background:

  • Accurate electron density distributions (EDD) are crucial for understanding chemical bonding.
  • Multipole refinement is a common method for deriving EDD from experimental diffraction data.
  • Previous studies have explored the accuracy of EDD extraction, but limitations in non-centrosymmetric systems remain.

Purpose of the Study:

  • To investigate the reliability of multipole refinement for extracting electron density distributions (EDD).
  • To assess the impact of experimental errors on the quality of derived EDD.
  • To determine the feasibility of obtaining accurate interaction densities from X-ray diffraction data for non-centrosymmetric crystals.

Main Methods:

  • Utilized CRYSTAL95 package for initial density function calculation.

Related Experiment Videos

  • Convoluted stockholder-partioned densities with thermal smearing functions from neutron diffraction.
  • Performed POP multipole refinement on urea crystal structure factors.
  • Introduced random errors to structure factors to simulate experimental conditions.

    • Main Results:

    • Achieved a good fit (R=0.6%) with initial structure factors, preserving interaction density characteristics.
    • Refinement with added random errors resulted in a poorer fit (R=1.1%) and a deformed interaction density.
    • Repetitions with different random errors yielded significantly different interaction density distributions.
    • The fitted EDD showed characteristics of the interaction density.

    Conclusions:

    • Multipole refinement can provide a good fit to experimental data.
    • However, the derived interaction density is highly sensitive to errors in structure factors.
    • Accurate interaction densities cannot be reliably obtained from X-ray diffraction data for non-centrosymmetric crystals.