Structures and parameters¶

A structure describes the crystal: its symmetry, unit-cell geometry and atom sites. Experiments link the structures that contribute to their calculated data.

The shared Structure chapter explains the scientific model; the steps below describe this interface.

Inspect a loaded structure¶

import edi

project = edi.Project.load('path/to/project')

for structure in project.structures:
    print(structure.name)
    print(structure.space_group.name_h_m)
    print(structure.cell.length_a.value)

Cell lengths and angles are parameters with values. A space-group name selects symmetry; it is not a floating-point fit parameter.

Read and change a parameter¶

For a project with at least one structure:

structure = project.structures[0]
length_a = structure.cell.length_a

print(length_a.value)
print(length_a.free)
length_a.free = True

The free flag allows a parameter to vary during a fit. Set it only when that parameter belongs in the scientific model you intend to fit. Setting free = True on a value a fit cannot vary raises an error that gives the reason. On a value set by symmetry or a constraint, it is ignored with a warning and the value stays dependent. Shared parameter concepts explain values, uncertainties and constraints.

Inspect the free set¶

for parameter in project.free_parameters:
    print(parameter.name, parameter.value, parameter.units)

This project-level list includes structural and experimental parameters. It helps you review the analysis before running a fit.

Read a structure file¶

The factory reads a structure from a CIF or .edi file, and the project's collection reads one and adds it:

structure = edi.StructureFactory.from_cif_path('structure.cif')
project.structures.add_from_cif_path('structure.cif')

from_cif_str and add_from_cif_str take the text instead of a path.

This creates a structure object; it does not by itself create a complete measurement and analysis project. Imported values start fixed. Items in the file that EasyDiffraction does not read come back as Python warnings starting with crysta.schema.cif_items_not_read, and a file EasyDiffraction cannot read raises an error that names the item. See CIF files.

For a complete runnable analysis, start from a project or a checked example. These pages intentionally document a demonstrated subset rather than claiming that all constructors and file variants are covered.

Compare Python paths with GUI labels, Edi keys and CIF names.