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

Area of Science:

• Crystallography
• Quantum Chemistry
• Materials Science

Background:

• Accurate electron density distribution is crucial for understanding chemical bonding.
• Urea is a fundamental molecule with significant biological and industrial applications.
• Previous studies have explored urea's electronic structure with varying levels of precision.

Purpose of the Study:

• To precisely determine the electron-density distribution in urea using high-resolution X-ray diffraction.
• To compare experimental results with theoretical calculations from various quantum chemical methods.
• To validate the accuracy of different computational approaches for describing molecular electronic structure.

Main Methods:

• High-precision single-crystal X-ray diffraction at 148 K.
• Application of experimental correction for thermal diffuse scattering (TDS).
• Refinement using the Hansen & Coppens multipole model.
• Quantum chemical calculations: Hartree-Fock (HF), DFT/LDA, and DFT/GGA.

Main Results:

• Excellent agreement was found between experimental deformation densities and structure factors and theoretical results.
• Density-functional theory (DFT) calculations showed slightly better agreement than Hartree-Fock (HF) calculations.
• Experimental displacement parameters closely matched neutron diffraction results.

Conclusions:

• High-precision X-ray diffraction provides an accurate experimental determination of urea's electron density.
• DFT methods, particularly GGA, offer a reliable and accurate approach for theoretical studies of urea's electronic structure.
• The study validates the use of multipole modeling for detailed charge density analysis.