Glossary¶

These terms are shared by the application, Python library and command line. The interface changes how you work with them, rather than changing their scientific meaning.

Project and model¶

Term	Meaning
Project	The complete analysis: structures, experiments, data, analysis settings and saved results. A project can be kept as a folder or a `.zip` archive.
Structure	A crystallographic model of a phase, including its space group, unit cell and atom sites.
Experiment	The observation or simulation associated with an instrument model, profile, background and contributing structures.
Parameter	A model quantity such as a cell length, atom coordinate, scale or profile coefficient. Any such parameter may be free or fixed.
Constraint	A declared relationship that reduces independent freedom between model quantities. A tied value is not another independently fitted parameter.

Experiment types and labels¶

These coloured labels mark the attributes of a measurement. They are generated from the experiment registry and shared by the app, the example catalogue and the guides.

An experiment combines one label from each family below. For example, the first fitting is pd neut cwl. Choose the measurement type before loading data; a listed attribute does not imply every combination is available.

Purpose¶

Label	Meaning
Fitting	Compare a calculated model with measured intensities and fit its parameters.
Simulation	Calculate the pattern from the current model without measured intensities.

Fitting mode¶

Label	Meaning
Single	Fit one experiment.
Joint	Fit several experiments together with shared model quantities.
Sequential	Fit a scan in order, using the preceding result as the next starting point.
Independent	Fit each dataset from the same starting model.

Sample form¶

Label	Meaning
pd	Diffraction from many crystallite orientations, usually measured as an intensity profile.
sc	Diffraction from an oriented crystal, measured as individual reflection intensities.

Probe¶

Label	Meaning
neut	Diffraction using neutrons; nuclear scattering and, where modelled, magnetic scattering contribute.
xray	Diffraction using X-rays; the scattering model depends on the electron distribution.

Beam mode¶

Label	Meaning
cwl	A specified incident wavelength; powder patterns are commonly expressed against 2θ.
tof	Neutron wavelengths are separated by arrival time. Calibration relates flight time to diffraction geometry.

Scattering type¶

Label	Meaning
Bragg	Model the crystalline contribution from lattice reflections.

Structure¶

Label	Meaning
Crystal	Atoms, their positions and displacements in the unit cell.
Magnetic	A crystal structure whose magnetic atoms also carry moments, related by magnetic symmetry.

Interface¶

Label	Meaning
AI assistant	An assistant such as ChatGPT or Claude sets up and fits the project from your request.

Analysis¶

Term	Meaning
Calculation or simulation	Evaluation of the model with its present parameter values. A simulation may use a calculation range without measured observations.
Fit	Optimisation of the chosen free parameters against measured observations.
Residual	The difference between observed and calculated signal. Its pattern can reveal systematic disagreement that a single agreement factor hides.
Standard uncertainty	The uncertainty reported with an estimated parameter or observation. A fitted uncertainty reflects the assumptions of the fit, rather than every possible systematic error.

Patterns and crystallographic quantities¶

Term	Meaning
Reflection	Diffraction associated with a set of lattice planes. A Bragg-position mark indicates where that reflection is expected in the pattern.
Background	The slowly varying contribution under diffraction peaks, represented by the background model chosen for the experiment.
Unit cell	The repeating geometry described by cell lengths and angles.
Fractional coordinates	A position expressed relative to the unit cell.
Space group	The crystallographic symmetry. Its setting identifies the coordinate convention used to describe that symmetry and the atom positions.
Occupancy	The occupation of an atom site.
Atomic displacement parameters (ADPs)	Displacement around an atom's average position. Isotropic and anisotropic representations use different parameters.
Scale factor	The weight of a structure's contribution to an experiment's calculated intensity. Its scientific interpretation depends on the experiment model and phase conventions.

Files and dictionaries¶

Term	Meaning
Edi (`.edi`)	EasyDiffraction's saved project format. It uses readable CIF-like syntax with keys that describe the project model.
CIF	Crystallographic Information File, a scientific exchange format with dictionaries maintained by the IUCr. A structural CIF and a complete Edi project serve different purposes.
coreCIF, pdCIF, magCIF	Dictionaries of general crystallographic, powder-diffraction and magnetic-structure quantities. Edi project keys are EasyDiffraction's project names, mapped to these where one applies.