PredictPeaks dialog.
Table of Contents
Using a known crystal lattice and UB matrix, predict where single crystal peaks should be found in detector/TOF space. Creates a PeaksWorkspace containing the peaks at the expected positions.
| Name | Direction | Type | Default | Description |
|---|---|---|---|---|
| InputWorkspace | Input | Workspace | Mandatory | An input workspace (MatrixWorkspace, MDEventWorkspace, or PeaksWorkspace) containing: - The relevant Instrument (calibrated as needed). - A sample with a UB matrix. - The goniometer rotation matrix. |
| WavelengthMin | Input | number | 0.1 | Minimum wavelength limit at which to start looking for single-crystal peaks. |
| WavelengthMax | Input | number | 100 | Maximum wavelength limit at which to stop looking for single-crystal peaks. |
| MinDSpacing | Input | number | 1 | Minimum d-spacing of peaks to consider. Default = 1.0 |
| MaxDSpacing | Input | number | 100 | Maximum d-spacing of peaks to consider. |
| ReflectionCondition | Input | string | Primitive | Which reflection condition applies to this crystal, reducing the number of expected HKL peaks? Allowed values: [‘Primitive’, ‘C-face centred’, ‘A-face centred’, ‘B-face centred’, ‘Body centred’, ‘All-face centred’, ‘Rhombohedrally centred, obverse’, ‘Rhombohedrally centred, reverse’, ‘Hexagonally centred, reverse’] |
| HKLPeaksWorkspace | Input | PeaksWorkspace | Optional: An input PeaksWorkspace with the HKL of the peaks that we should predict. The WavelengthMin/Max and Min/MaxDSpacing parameters are unused if this is specified. | |
| RoundHKL | Input | boolean | True | When using HKLPeaksWorkspace, this will round the HKL values in the HKLPeaksWorkspace to the nearest integers if checked. Keep unchecked to use the original values |
| OutputWorkspace | Output | PeaksWorkspace | An output PeaksWorkspace. |
This algorithm will predict the position of single-crystal diffraction peaks (both in detector position/TOF and Q-space) and create an output PeaksWorkspace containing the result.
This algorithm uses the InputWorkspace to determine the instrument in use, as well as the UB Matrix and Unit Cell of the sample used. You can use the CopySample v1 algorithm (with CopyLattice=1) to copy a UB matrix from a PeaksWorkspace to another workspace.
The algorithm operates by calculating the scattering direction (given the UB matrix) for a particular HKL, and determining whether that hits a detector. The Max/MinDSpacing parameters are used to determine what HKL’s to try.
The parameters of WavelengthMin/WavelengthMax also limit the peaks attempted to those that can be detected/produced by your instrument.
If you specify the HKLPeaksWorkspace parameter, then the algorithm will use the list of HKL in that workspace as the starting point of HKLs, instead of doing all HKLs within range of Max/MinDSpacing and WavelengthMin/WavelengthMax.
A typical use case for this method is to use FindPeaksMD v1 followed by IndexPeaks v1 to find the HKL of each peak. The HKLs found will be floats, so specify RoundHKL=True in PredictPeaks to predict the position at the exact integer HKL. This may help locate the center of peaks.
Another way to use this algorithm is to use CreatePeaksWorkspace v1 to create a workspace with the desired number of peaks. Use python or the GUI to enter the desired HKLs. If these are fraction (e.g. magnetic peaks) then make sure RoundHKL=False.
See also
Algorithm PredictFractionalPeaks v1
Categories: Algorithms | Crystal