Rietveld fit: CeCoAl₃, POLARIS¶

The same staged fit as the Python and Command line tutorials, in the app. Its structure and experiment come from EasyDiffraction's collection with Load ▾ From web…, and each stage frees its parameters in the Parameters table on Analysis before the fit.

Create a project¶

Press Start on Home, then Create a new project, and give it a name.

Load the structure¶

On Structure, choose Load ▾ From web…, search for each entry by its id and click it:

• pd-neut-tof_cecoal-polaris-cecoal

Load the experiment¶

On Experiment, choose Load ▾ Full experiment From web…, search for each entry by its id and click it:

• pd-neut-tof_cecoal-polaris-polaris

Set the minimizer¶

On Analysis → Extra, set the Minimizer as the case's project does: the Shift/s.u. stop rule and room for more iterations.

Start with nothing free¶

On Analysis, open the Free column header of the Parameters table and fix every parameter, so the stages below free one group at a time.

Scale, time-of-flight calibration and cell¶

The scale, the DIFC offset and its quadratic term, and the three cell lengths put the peaks in place and at the right height.

Filter the Linked structures and Cell parameters, one category at a time, using the category filter and the Instrument parameters using the category filter, click the Free column header and choose Free · all; then type linear in the name filter and choose Fixed · all in the same menu, then press Fit in the status bar.

Background¶

The first twelve polynomial terms (orders 0 to 11) follow the level between the peaks; the higher ones stay at zero.

Tick Free for the first 12 Background coefficients, then press Fit in the status bar.

Peak widths¶

Filter the Peak broadening parameters with gamma_1 in their name using the category filter and the name filter and the Peak broadening parameters with sigma_1 in their name using the category filter and the name filter, click the Free column header and choose Free · all, then press Fit in the status bar.

Atom positions¶

The coordinates the symmetry leaves free.

Filter the Atomic coordinates parameters using the category filter, click the Free column header and choose Free · all, then press Fit in the status bar.

Displacements¶

Filter the Atomic displacement parameters using the category filter, click the Free column header and choose Free · all, then press Fit in the status bar.

Absorption¶

Absorption weakens the intensities with time of flight, as the displacements do with angle, so it comes after them, on its own.

Filter the Absorption parameters using the category filter, click the Free column header and choose Free · all, then press Fit in the status bar.

Al3 occupancy¶

Last, Al3's occupancy, which moves with its displacement.

Filter the Atomic occupancies parameters with [Al3] in their name using the category filter and the name filter, click the Free column header and choose Free · all, then press Fit in the status bar.

Correlations¶

The Correlations view on Analysis shows which fitted parameters move together.

Report¶

The Report page collects the structure, the experiment and the fit.