structure-2d-hexagonal-crystal-npt


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structure-2d-hexagonal-crystal-npt
Property Definition ID
The full Property Definition identifier using the Tag URI scheme.
tag:staff@noreply.openkim.org,2015-05-26:property/structure-2d-hexagonal-crystal-npt
Title
A brief one-sentence description of this Property Definition.
Equilibrium two-dimensional layer hexagonal crystal structure at a given temperature and stress state
Description
A description about this Property Definition.
Conventional lattice parameter and basis atoms of a two-dimensional hexagonal crystalline layer at a given temperature and stress state.
Contributor
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ilia
Maintainer
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ilia
Creation date
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2015-05-26
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a

typefloat
has-unittrue
extent[]
requiredtrue
descriptionThermal average length of unit cell vectors <a> and <b> (which are equal for this crystal structure). The two associated directions correspond to the first and second components of the entries of 'basis-atom-coordinates'. The lattice does not repeat in a third direction, but the basis vector <c> used to define out-of-plane atomic coordinates is taken to be orthogonal to <a> and <b> and equal in length to them. The triad (<a>,<b>,<c>) forms a right-handed system.

basis-atom-coordinates

typefloat
has-unitfalse
extent[":" 3]
requiredtrue
descriptionFractional coordinates of the basis atoms in the conventional unit cell. If the unit cell vectors are denoted by <a> and <b>, the third basis vector, <c>, is taken to be orthogonal to <a> and <b> and equal in length to them, such that the triad (<a>,<b>,<c>) forms a right-handed system. If the fractional coordinates of atom 'i' are [afrac_i, bfrac_i, cfrac_i], the value of 'basis-atom-coordinates' will be of the form [[afrac_1 bfrac_1 cfrac_1] [afrac_2 bfrac_2 cfrac_2] ... ]. The first two components of each basis atom must be between zero and one, inclusive of zero. The third component can be any real number, since it is normalized relative to an unrelated in-plane length, and may be positive or negative in order to accomodate the standard Wyckoff positions for layer groups.

cauchy-in-plane-stress

typefloat
has-unittrue
extent[3]
requiredtrue
descriptionThe [xx,yy,xy] (i.e. [11,22,12]) components of the Cauchy in-plane stress (force-per-unit-length) acting on the periodic cell. The orthonormal basis (<e_1>, <e_2>) used to express the stress should be such that e_1 is in the direction of <a>, and e_2 is in the direction of the vector product of <c> and <a> (<c> x <a>). The form must be [d d 0] to maintain the symmetry.

species

typestring
has-unitfalse
extent[":"]
requiredtrue
descriptionThe element symbols of the basis atoms. The order in which the species are specified must correspond to the order of the atoms listed in 'basis-atom-coordinates'.

temperature

typefloat
has-unittrue
extent[]
requiredtrue
descriptionTemperature of the 2-d crystal.

layer-group

typestring
has-unitfalse
extent[]
requiredfalse
descriptionHermann-Mauguin designation for the layer group associated with the symmetry of the crystal (e.g. p6/mmm for graphene).

short-name

typestring
has-unitfalse
extent[":"]
requiredfalse
descriptionShort name defining the 2-d hexagonal crystal type.

wyckoff-coordinates

typefloat
has-unitfalse
extent[":" 3]
requiredfalse
descriptionCoordinates of the unique Wyckoff sites used in the fully symmetry-reduced description of the crystal, given as fractions of the lattice vectors and the third basis vector <c>, defined to be perpendicular to the two lattice vectors and equal in length to <a>, such that the triad (<a>,<b>,<c>) forms a right-handed system. The order of elements in this array must correspond to the order of the entries listed in 'wyckoff-species' and 'wyckoff-multiplicity-and-letter'.

wyckoff-multiplicity-and-letter

typestring
has-unitfalse
extent[":"]
requiredfalse
descriptionMultiplicity and standard letter of the unique Wyckoff sites used in the fully symmetry-reduced description of the crystal (e.g. 2b is the only entry for graphene). Note that the sum of the Wyckoff multiplicities should equal the total number of elements in 'basis-atom-coordinates'. The order of elements in this array must correspond to the order of the entries listed in 'wyckoff-species' and 'wyckoff-coordinates'.

wyckoff-species

typestring
has-unitfalse
extent[":"]
requiredfalse
descriptionThe element symbol of the atomic species of the unique Wyckoff sites used in the fully symmetry-reduced description of the crystal. The order of the entries must correspond to the order of the entries in 'wyckoff-multiplicity-and-letter' and 'wyckoff-coordinates'.


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