Manual bandwidths

For many patterns the automated search pressing F5 on your keyboard will derive so many bandwidths that the number of lattice points might be sufficient to predict the Bravais lattice type as well as the lattice parameters.

If the automatic search does not assign a bandwidth for all – or in the case of complicated phases even for very many – bands, missing bandwidths must or should be set manually. Otherwise, there is a risk that a superlattice will be described by mistake. The procedure for manual assignment is identical to what is done in principle during the automatic search.

Procedure

  1. Mandatory: Switch on the radio button “All with” (main vertical menu / section “Pole”).
  2. Recommended: Switch on the radio button “Zone” in section “Band edges”, since only then traces (and band edges) of a selcted zone are displayed.
    Please keep in mind, where the selected band in the gnomonic projection was, since only there you can jump from zone axis to zone axis in order to see where are still not defined bandwidths.
  3. If you select a zone axis [uvw] of which
    a) more than two (hkl) intersect,
    b) of which at least one bandwidth is defined, and
    c) for at least one band no bandwidth is defined,
    the trace of one band without bandwidth of them is colored white.
    A band of known width is shown by the yellow trace and a third is colored in blue.
    You can assign the white color to another trace without bandwidth by selecting this trace by Ctrl+RMB (right mouse button).
    If you only press RMB (without Ctrl), the active trace becomes blue.
    The yellow reference trace you can assign by Shift+LMB.
  4. When you press “a” on your keyboard, a bandwidth for the white curve is calculated from the yellow and blue traces.
    If you like to solve other bandwidths, continue with 3.
  5. If the calculated bandwidth is obviously wrong, e.g. because the first order (in the profile window the first vertical dashed line seen from the center), does not match the green lines indicating the extreme position of the 1st derivative (red graph), press “d” to decline this solution.
    Press also “d” if the vertical dashed and green lines do not even approximately match.
  6. Try another combination of blue and yellow traces, or switch to a different zone axis on the white line.

The selection of bandwidths can be challenging sometimes. However, since already asymmetric band edges with θasym>0.1° (see Band profile window) are excluded, many false bands are suppressed per default.

Please note: An improperly defined band can be removed by selecting the trace of (hkl) (Shift+LMB), or the pole [hkl]* (Ctrl+LMB) in the Funk transformation, or even the reciprocal lattice point (Crtl+LMB) in the Reciprocal lattice window and pressing “r”. Then, however, all bands will be removed which use this band as reference since the calculation is based on this band.
For totally wrong bands this will not have any consequence since then all derived bands are also wrong. Only if the “first order rule” has been ignored, many bands can be affected. But in that case, the horizontal bars in the Funk transformation would be extremely long since they indicate the deviation between the extrema of the 1st derivative of the band profile and the “first” interference order. In so far, it is only consequent to remove all bandwidths affected by this improper one.

Please note: The “first” interference order is only apparently the first. In fact it should show the best agreement with the maximum positions of the 1st derivation. If the first interference order is not the strongest, this can lead to (admittedly justified) irritations.