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Type HKLF data tree entries: Single Crystal

Single-crystal datasets are read into GSAS-II using the Import/Structure Factor menu command, since the histogram is a table of structure factors. Note that GSAS-II can fit a structure (phase entry) to a one single crystal histogram, but it is also possible to fit a phase to multiple single-crystal histograms (which might be collected at different wavelengths) or even a combination of single-crystal and powder datasets (as might be the case with a laboratory single-crystal measurement combined with a neutron powder diffraction histogram.)

What can I do here?

You can change the weight factor. This is a multiplier on all of the reflection weights in this histogram. Rarely needs to be changed. Use of 1 for all datasets provides optimal statistical weighting, unless there is systematic error present.

  • Error Analysis - this produces a 'normal probability' plot for the refinement result as bounded by the limits. The slope and intercept of the curve in the central region (-1 < / < 1) are shown on the plot status line. The slope is the GOF for the best fit set of data points (~68% of the data).
  • Merge HKLs - this combines equivalent/duplicate reflections according to space group and some options to make a unique and averaged set of structure factors.
  • Plot 1D HKLs - shows a stick diagram scaled to \(\rm F_c^2\) for the reflection for the selected phase
  • Plot HKLs (the default plot) - shows a HKL layer with rings scaled to \(\rm F\) or \(\rm F^2\) for \(\rm F_o\) and \(\rm F_c\).
    • +/- steps through the layers
    • h,k or l selects the orientation
    • see K box for all the possible commands.
  • Plot 3D HKLs - shows a 3D representation of the unique part reciprocal space points for this phase. The save as/key item in the plot status bar shows the various commands for modifying this plot.

Instrument Parameters

This window shows the histogram type (SXC or SNC, for x-ray and neutron, respectively) and the wavelength. You may change the wavelength or radiation type but rarely will need to do so.

Reflection List

This window shows the reflections for this single crystal data set.

What can I do here?

  • Menu 'Reflection List' – some items are useful for SHKL (single crystal) histograms.
    • Select phase – if there is more than one phase; you can select another phase; the window title will show which phase is shown. You can also simply select the tab for the desired phase.
    • Plot 1D HKLs – shows a stick diagram scaled to \(\rm F_c^2\) for the reflection for the selected phase
    • Plot HKLs (the default plot)– shows a HKL layer with rings scaled to \(\rm F\) or \(\rm F^2\) for \(\rm F_o\) and \(\rm F_c\).
      • +/- steps through the layers
      • h,k or l selects the orientation
      • see K box for all the possible commands.
    • Plot 3D HKLs – shows a 3D representation of the unique part reciprocal space points for this phase. The save as/key item in the plot status bar shows the various commands for modifying this plot.
    • Wilson statistics – displays a Wilson plot for the intensities.
    • Show/hide extinct reflections – can exclude space group extinctions from the list

What is plotted here?

By default, the plot will show a l=0 layer of reflections on a square grid as rings proportional to \(\rm F_o\) (blue), \(\rm F_c\) (green) and a central dot (green or red) proportional to \(\rm (F_o - F_c)\).

What can I do with the plot?

The "K" box in the plot controls shows the 14 keystroke controls for the plot – they are generally self-explanatory.