Co₂SiO₄ on D20¶
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_cosio-d20-cosio
Load the experiment¶
On Experiment, choose Load ▾ Full experiment From web…, search for each entry by its id and click it:
pd-neut-cwl_cosio-d20-d20
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 sets the overall height of the pattern, and the zero shift and the three cell lengths put the peaks where they are measured.
Filter the Linked structures and Cell parameters, one category at a time, using the category filter and 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¶
With the peaks in place, the fourteen background points follow the level between them.
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¶
The profile terms now fit the widths and shapes of the peaks. diffraction-lib's tutorial also fits a peak asymmetry; this case's profile has none.
Filter the Peak profile 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.
Atom positions¶
The peak intensities now depend mostly on where the atoms are. Co1 sits on a centre of symmetry and the other sites on the mirror plane, so only their free coordinates are fitted.
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¶
The displacements change the intensities more at high angle.
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.
Constrain the two Co sites¶
The correlations show no strong pair for the two Co sites, yet the fit gives them very different displacements, Co1's even negative, which no atom can have: both are Co and scatter alike, so the pattern cannot tell their thermal motions apart. Give each an alias and constrain Co2's to follow Co1's, starting again from 0.5 Ų, then fit again; the shared displacement is positive and its s.u. smaller than either had alone.
Filter the Atomic displacement parameters with [Co2] in their name using the category filter and the name filter, click the Free column header and choose Fixed · all, then press Fit in the status bar.
Oxygen occupancies¶
Last, the oxygen occupancies, which change the intensities as the displacements do.
Filter the Atomic occupancies parameters with [O 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.
