Phase problem
Shift in real space
Centrosymmetric vs. Acentric
Interactive examples
Single atom
Pair of atoms
One atom in unit cell
Two atoms in unit cell
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Contents

This time you can create a pair of atoms on the Xaxis. You are
free to choose identical or different atoms at any position on the
Xaxis. The positions of the atoms/electrons are given in A. You
can also select whether to
calculate Xray or neutron intensities. The calculated range for
the scattering intensity h is fixed to 2.0Å^{1}
to 2.0Å^{1} parallel to the xaxis.
Start exploring and try to answer the questions below:
 What is the effect of the positions /type on the intensity, the
real part, the imaginary part and the phase angle of the
diffraction pattern ?
 What is the difference between a centrosymmetric structure
and a noncentrosymmetric ?
 Simulate two identical atoms at identical distance left and
right from the origin. Now shift both atoms by the same amount.
This pair of atoms is still centrosymmetric, with the center
of symmetry in the middle of the atoms. Why is the phase
angle no longer that of a centrosymmetric structure ?
 Try to work out the relationship between the magnitude of the
interatomic distance and the phase angle ?
 Why does the phase angle change periodically, although the
other features of the diffraction pattern do not ?
Once you are done, click
here to verify your answers.
