NXem_ebsd_crystal_structure_model

Status:

base class, extends NXobject

Description:

Crystal structure phase models used for indexing Kikuchi pattern.

This base class contains key metadata relevant to every physical kinematic or dynamic diffraction model to be used for simulating Kikuchi diffraction pattern. The actual indexing of Kikuchi pattern however maybe use different algorithms which build on these simulation results but evaluate different workflows of comparing simulated and measured Kikuchi pattern to make suggestions which orientation is the most likely (if any) for each scan point investigated.

Traditionally Hough transform based indexing has been the most frequently used algorithm. More and more dictionary based alternatives are used. Either way both algorithm need a crystal structure model.

Symbols:

n_hkl: Number of reflectors (Miller crystallographic plane triplets).

n_pos: Number of atom positions.

Groups cited:

none

Structure:

crystallographic_database_identifier: (optional) NX_CHAR

Identifier of an entry from crystallographic_database which was used for creating this structure model.

crystallographic_database: (optional) NX_CHAR

Name of the crystallographic database to resolve crystallographic_database_identifier e.g. COD or others.

unit_cell_abc: (optional) NX_FLOAT (Rank: 1, Dimensions: [3]) {units=NX_LENGTH}

Crystallography unit cell parameters a, b, and c.

unit_cell_alphabetagamma: (optional) NX_FLOAT (Rank: 1, Dimensions: [3]) {units=NX_ANGLE}

Crystallography unit cell parameters alpha, beta, and gamma.

unit_cell_volume: (optional) NX_FLOAT {units=NX_VOLUME}

Volume of the unit cell

space_group: (optional) NX_CHAR

Crystallographic space group

is_centrosymmetric: (optional) NX_BOOLEAN

True if space group is considered a centrosymmetric one. False if space group is considered a non-centrosymmetric one. Centrosymmetric has all types and combinations of symmetry elements (translation, rotational axis, mirror planes, center of inversion) Non-centrosymmetric compared to centrosymmetric is constrained (no inversion). Chiral compared to non-centrosymmetric is constrained (no mirror planes).

is_chiral: (optional) NX_BOOLEAN

True if space group is considered a chiral one. False if space group is consider a non-chiral one.

laue_group: (optional) NX_CHAR

Laue group

point_group: (optional) NX_CHAR

Point group using International Notation.

unit_cell_class: (optional) NX_CHAR

Crystal system

Any of these values:

  • triclinic

  • monoclinic

  • orthorhombic

  • tetragonal

  • rhombohedral

  • hexagonal

  • cubic

phase_identifier: (optional) NX_UINT {units=NX_UNITLESS}

Numeric identifier for each phase. The value 0 is reserved for the unknown phase essentially representing the null-model that no phase model was sufficiently significantly confirmed. Consequently, the value 0 must not be used as a phase_identifier.

phase_name: (optional) NX_CHAR

Name of the phase/alias.

atom_identifier: (optional) NX_CHAR (Rank: 1, Dimensions: [n_pos])

Labels for each atom position

atom: (optional) NX_UINT (Rank: 1, Dimensions: [n_pos]) {units=NX_UNITLESS}

The hash value \(H\) is \(H = Z + N*256\) with \(Z\) the number of protons and \(N\) the number of neutrons of each isotope respectively. Z and N have to be 8-bit unsigned integers. For the rationale behind this M. Kühbach et al. (2021)

atom_positions: (optional) NX_FLOAT (Rank: 2, Dimensions: [n_pos, 3]) {units=NX_LENGTH}

Atom positions x, y, z.

atom_occupancy: (optional) NX_FLOAT (Rank: 1, Dimensions: [n_pos]) {units=NX_DIMENSIONLESS}

Relative occupancy of the atom position.

number_of_planes: (optional) NX_UINT {units=NX_UNITLESS}

How many reflectors are distinguished. Value has to be n_hkl.

plane_miller: (optional) NX_NUMBER (Rank: 2, Dimensions: [n_hkl, 3]) {units=NX_UNITLESS}

Miller indices \((hkl)\).

dspacing: (optional) NX_FLOAT (Rank: 1, Dimensions: [n_hkl]) {units=NX_LENGTH}

D-spacing.

relative_intensity: (optional) NX_FLOAT (Rank: 1, Dimensions: [n_hkl]) {units=NX_DIMENSIONLESS}

Relative intensity of the signal for the plane.

Hypertext Anchors

List of hypertext anchors for all groups, fields, attributes, and links defined in this class.

NXDL Source:

https://github.com/FAIRmat-Experimental/nexus_definitions/tree/fairmat/contributed_definitions/NXem_ebsd_crystal_structure_model.nxdl.xml