Interactive Tutorial about Diffraction Interactive example: Finite size effect 

Reciprocal space
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When calculating intensities based on a structural model, the crystal
should extend to infinity, otherwise the Fourier transform is truncated,
resulting in ripples. This is also referred to as
size effect. However, by choosing the correct grid in reciprocal
space, these ripples can be avoided by choosing a grid coinciding with
the nodes of the "ripples". This examples allows one to explore this
concept.
The controls in the simulator allow you to specify the size of a model crystal and the range and grid in reciprocal space (hkplane) that will be calculated. Since the simulated crystals have a finite size the scattering pattern will in general contain contributions cause by the limited size of the crystal. A detailed discussion is given the DISCUS Users Guide. A simple recipe for selecting a suitable grid in reciprocal space is given below:

© Th. Proffen and R.B. Neder, 2003 