GeneratingDPs.htmlTEXTStMl>77 a CrystalDiffract Online Help

Generating Diffraction Patterns


CrystalDiffract calculates a diffraction pattern using structural information (lattice parameters, atom types and coordinates) saved in a CrystalMaker binary file, combined with information about site occupancies, radiation wavelength and type, peak profile, etc.

To calculate the intensity of a single reflection, CrystalMaker performs the following steps:-

  1. Calculate structure factor (a complex number with real and imaginary parts) using all atoms in the unit cell and their appropriate atomic scattering factors (or neutron scattering lengths)
  2. Calculate Lorentz polarisation factor (Lp)
  3. Calculate intensity as the complex conjugate of the structure factor, scaled by the Lorenz factor

The intensities are scaled so that they correspond to the amount scattered by one cubic centimetre of solid material.

To calculate a full diffraction pattern, the individual intensities of all calculated reflections need to be combined into a single, continuous function of intensity versus two-theta:-

  1. Correct intensities for the multiplicity of each reflection
  2. Merge all reflections with the same d-spacing
  3. Calculate diffraction profile by convoluting the peak positions with the appropriate peak profile type (e.g., Gaussian, Lorentzian, etc.)


Displaying a Film or Graph

You can use the Plot menu to choose between plotting a graph of intensity versus two-theta, or plotting a grey-scale film:-


Changing the Radiation Wavelength

The Wavelength dialog lets you change the radiation's wavelength and properties:-


Specifying X-rays or Neutrons

You can choose to "use" X-rays or neutrons by selecting the appropriate command from the Diffract menu.

If a diffraction pattern is already displayed, selecting a different radiation type will cause the diffraction pattern to be recalculated in the same window.

If you wish to compare the x-ray and neutron diffraction patterns for the same material:-

  1. Display a diffraction pattern using X-rays
  2. Hold down the option key (sometimes labelled "alt") on your keyboard, and select the Neutrons command from the Diffract menu.
    A new window will open, displaying the neutron diffraction pattern for your material.


Printing a Diffraction Pattern

To print a diffraction pattern, first select the appropriate diffraction window, then choose the Print command from the File menu. The printed pattern is scaled to the full paper size, and printed at high-resolution (up to 300 dpi for PostScript printers).


Main Menu

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