2.3.3.3.207. NXunit_cell

Status:

base class, extends NXobject

Description:

Description of a unit cell, i.e., the crystal structure of a single ...

Description of a unit cell, i.e., the crystal structure of a single thermodynamic phase.

Symbols:

n_pos: Number of atom positions.

Groups cited:

none

Structure:

crystallographic_database_identifier: (optional) NX_CHAR

Identifier of an entry resolvable via crystallographic_database ...

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

crystallographic_database: (optional) NX_CHAR

Name of the crystallographic database to resolve ...

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

lattice_system: (optional) NX_CHAR

A lattice system is a group of lattices with the same set of lattice point gro ...

A lattice system is a group of lattices with the same set of lattice point groups. For further information, see https://en.wikipedia.org/wiki/Crystal_system.

Any of these values:

  • triclinic

  • monoclinic

  • orthorhombic

  • tetragonal

  • rhombohedral

  • hexagonal

  • cubic

space_group: (optional) NX_CHAR

Crystallographic space group. ...

Crystallographic space group. A space group is the symmetry group of a repeating pattern in space. For further information, see International Table for Crystallography (https://it.iucr.org/).

point_group: (optional) NX_CHAR

Crystallographic point group. ...

Crystallographic point group. A crystallographic point group is a set of symmetry operations, corresponding to one of the point groups in three dimensions, such that each operation (perhaps followed by a translation) would leave the structure of a crystal unchanged. This field should use Schoenflies notation (see Schoenflies, A., Krystallsysteme und Krystallstructur, 1891). For further information, see https://dictionary.iucr.org/Point_group.

laue_group: (optional) NX_CHAR

Laue group (also called Laue class). ...

Laue group (also called Laue class). The Laue classes are eleven geometric crystal classes containing centrosymmetric crystallographic types of point groups and their subgroups. When absorption is negligible and Friedel’s law applies, it is impossible to distinguish by diffraction between a centrosymmetric point group and one of its non-centrosymmetric subgroups; only point groups belonging to different Laue classes can then be distinguished. For further information, see https://dictionary.iucr.org/Laue_class.

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

Crystallography unit cell parameters a, b, and c

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

Crystallography unit cell vector a

@depends_on: (optional) NX_CHAR

For definining which coordinate system the unit cell vector a is defined in.

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

Crystallography unit cell vector b

@depends_on: (optional) NX_CHAR

For definining which coordinate system the unit cell vector b is defined in.

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

Crystallography unit cell vector c

@depends_on: (optional) NX_CHAR

For definining which coordinate system the unit cell vector c is defined in.

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

Crystallography unit cell angles alpha, beta, and gamma

volume: (optional) NX_FLOAT {units=NX_VOLUME}

Volume of the unit cell

is_centrosymmetric: (optional) NX_BOOLEAN

True if space group is considered a centrosymmetric one. ...

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. ...

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

phase_identifier: (optional) NX_UINT {units=NX_UNITLESS}

Identifier for the phase. ...

Identifier for the phase. The value 0 is reserved for the unknown phase which represents the null-model that no phase model was sufficiently significantly confirmed.

phase_name: (optional) NX_CHAR

Trivial 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 :math:`H` is :math:`H = Z + N \cdot 256` with :math:`Z` ...

The hash value \(H\) is \(H = Z + N \cdot 256\) 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.

@depends_on: (optional) NX_CHAR

Reference to an instance of NXcoordinate_system whereby the positions can be ...

Reference to an instance of NXcoordinate_system whereby the positions can be resolved.

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

Relative occupancy of the atom position.

depends_on: (optional) NX_CHAR

For definining which coordinate system the unit cell parameters are defined in.

Hypertext Anchors

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

NXDL Source:

https://github.com/FAIRmat-NFDI/nexus_definitions/tree/fairmat/contributed_definitions/NXunit_cell.nxdl.xml