Rietveld fit: LiNiO₂, ECHIDNA¶

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-cwl_lmo-echidna-lmo

Load the experiment¶

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

• pd-neut-cwl_lmo-echidna-echidna

Add the relations¶

The project ties some parameters together from the start. On Analysis → Extra, add the aliases and constraints.

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, 2θ zero and cell¶

The scale, the zero shift and the two 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 with offset 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.

Sample displacement and transparency¶

The sample sits a little off the diffractometer axis and the beam goes into it; both shift the peaks with angle, unlike the zero.

Filter the Instrument parameters with calib 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.

Background¶

The nine background points follow the level between the peaks.

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

Peak widths¶

Filter the Peak broadening parameters using the category filter, click the Free column header and choose Free · all; then type lorentz_x in the name filter and choose Fixed · all in the same menu, then press Fit in the status bar.

Oxygen position¶

O's height along c is the only coordinate 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¶

Li1's, Ni2's and O's; Ni1 and Li2 follow by the relations.

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.

Li/Ni mixing¶

Last, Li1's occupancy, which sets how much Ni sits on the Li site; it moves with the displacements, so it comes after them.

Filter the Atomic occupancies parameters with [Li1] 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.