Guides

Each guide does one task from start to finish. Its title names the task as “How to …”, and the menu names the task alone, since the tab already says it is a guide.

Each guide’s fits are a script in examples/guides/, run by the test suite, and the output a guide shows is what its script printed.

Before the fit

• How to check a pattern before fitting reads rietx.diagnose and draws the reflection ticks.

• How to limit the fit range or leave out a region sets two_theta_limits and PatternData.excluded_regions.

Instrument

• How to calibrate an instrument on a standard and reuse it saves the widths a standard measured and loads them for each sample.

Background and extra peaks

• How to use a measured blank as the background holds an empty-container scan under the pattern with BackgroundFixedPlusChebyshev.

• How to add a hump to the background declares a broad Gaussian for amorphous or container scattering.

• How to fit a peak from the sample holder declares a sharp line no phase explains with a PeakComponent.

Constraints and plans

• How to keep a parameter fixed whatever the plan frees uses Refinement.hold.

• How to tie parameters together makes parameters equal, or one a linear function of others.

• How to restrain a bond length or an angle adds chemistry as weighted observations.

• How to add a stage to a refinement plan edits a preset or builds a plan.

Running a fit

• How to run a plan one stage at a time uses Refinement.run_stage and a report at each stage.

• How to choose the next parameter to free reads Refinement.suggest and measures the move with compare_freed.

• How to branch a refinement, compare the branches and roll back uses Refinement.branch, RefinementTree.compare and Refinement.checkout.

• How to watch or stop a running fit uses rietx watch, a cancel token, and the switches that turn recording off.

Results

• How to find the weight fraction of each phase in a mixture reads result.qpa, checks a minor phase, and corrects for microabsorption.

• How to quote lattice parameters with their esds reads the cell, its volume and rx.format_su, and shows what the esd leaves out.

• How to quote a parameter that ended on its bound uses Refinement.profile_interval.

• How to export the refined structure as a CIF and the reflection list as a table uses Refinement.write_cif and Refinement.write_reflection_table.

Other programs

• How to open a GSAS, TOPAS or FullProf refinement and write one back uses rx.read_project_model and the four writers.

Series

• How to fit a temperature series chains one refinement per pattern with refine_sequential and reads a trajectory.

• How to check a series for path dependence runs the chain both ways and refits a flagged step from cold.

• How to refine a cell edge as a function of temperature refines an equation’s coefficients against every pattern at once.

Magnetic structures

• How to refit the nuclear model with the moment present takes the nuclear model from a pattern above the ordering temperature, or refits it with the moment in, and reads the moment after.

Several radiations

• How to fit an X-ray and a neutron pattern together refines one structure against both with MultiHistogramRefinement, and refines the neutron wavelength.