7 research outputs found
The Malaria Pigment Hemozoin Comprises at Most Four Different Isomer Units in Two Crystalline Models: Chiral as Based on a Biochemical Hypothesis or Centrosymmetric Made of Enantiomorphous Sectors
Powder X‑ray Diffraction Electron Density of Cubic Boron Nitride
Conventionally, the core electron
density (ED) of atoms in molecules
is considered to be virtually unperturbed by chemical bonding effects.
Here we report a combined experimental and theoretical investigation
of the ED of cubic boron nitride including a detailed modeling of
the core ED. By modeling structure factors obtained from very-high-resolution
synchrotron powder X-ray diffraction data, it is possible to model
not only the valence ED but also the response of the core ED to the
effects of chemical bonding. The biggest challenge when studying the
core ED is the deconvolution of the thermal motion from the experimental
structure factors, since the thermal motion is strongly correlated
to core ED deformation. However, atomic displacement parameters could
be estimated from a full pattern Rietveld-multipolar refinement, and
they are shown to be in good correspondence with ab initio lattice
dynamics calculations. The corresponding extended multipole model
including both core and valence ED refinement suggests that 2.0 electrons
are transferred from the boron atomic basin to the nitrogen atomic
basin. The core density was found to deplete upon bonding, which is
in line with a significant charge transfer