KSPACING: Difference between revisions
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{{TAGDEF|KSPACING|[real]|0.5}} | {{TAGDEF|KSPACING|[real]|0.5}} | ||
Description: The tag {{TAG|KSPACING}} determines the number of k | Description: The tag {{TAG|KSPACING}} determines the number of k points if the {{TAG|KPOINTS}} file | ||
is not present. | is not present. | ||
---- | ---- | ||
{{TAG|KSPACING}} is the smallest allowed spacing between k points in units of | {{TAG|KSPACING}} is the smallest allowed spacing between k points in units of <math>\AA^{-1}</math>. The number of k points increases when the spacing is decreased. | ||
<math>\AA^{-1}</math>. The number of k | The number of k points in the direction of the first, second and third reciprocal lattice vector is determined by <math> N= \mathrm{max}(1, | \vec{b}_i| / \mathrm{KSPACING} ). </math> | ||
The number of k | These values are rounded to the next integer greater than or equal to <math> N </math>. In this equation, <math> \vec{b}_i </math> are the reciprocal lattice vectors <math> \vec{b}_i \vec{a}_j = 2 \pi \delta_{ij} </math>. | ||
reciprocal lattice vector is determined by <math> N= \mathrm{max}(1, | \vec{b}_i| / \mathrm{KSPACING} ). </math> | The generated grid is either centred at the <math>\Gamma</math> point, i.e., includes the <math>\Gamma</math> point when ({{TAG|KGAMMA}}=.TRUE., or is shifted away from the <math>\Gamma</math> point, as done for Monkhorst-Pack grids when ({{TAG|KGAMMA}}=.FALSE.. The default is to include the <math>\Gamma</math> point. | ||
These values are rounded to the next integer greater than or equal to <math> N </math>. In this equation | {{NB|warning|This implementation is not entirely consistent with the automatic k-point generation (Mode{{=}}A) used in the {{FILE|KPOINTS}} file.}} | ||
<math> \vec{b}_i </math> | If the k points are generated using the automatic mode in the {{FILE|KPOINTS}} file, <math> N</math> is calculated as | ||
are the reciprocal lattice vectors <math> \vec{b}_i \vec{a}_j = 2 \pi \delta_{ij} </math>. | |||
The generated grid is either centred at the <math>\Gamma</math> point | |||
from the <math>\Gamma</math> point, as | |||
The default is to include the <math>\Gamma</math> point. | |||
(Mode=A) used in the KPOINTS file. If the k | |||
in the KPOINTS file, <math> N</math> is calculated as | |||
<math> N= \mathrm{max}(1, | \vec{b}_i| / (2 \pi \times \mathrm{KSPACING}) ) </math> | <math> N= \mathrm{max}(1, | \vec{b}_i| / (2 \pi \times \mathrm{KSPACING}) ) </math> | ||
and rounding is to the nearest integer. We recommend | and rounding is to the nearest integer. We recommend using the {{TAG|KSPACING}} tag in the {{FILE|INCAR}} file | ||
and | and avoiding the automatic mode via the {{FILE|KPOINTS}} file. | ||
== Related | == Related tags and articles == | ||
{{TAG|KGAMMA}} | {{TAG|KGAMMA}}, {{FILE|KPOINTS}} | ||
{{sc|KSPACING|Examples|Examples that use this tag}} | {{sc|KSPACING|Examples|Examples that use this tag}} | ||
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[[The_VASP_Manual|Contents]] | [[The_VASP_Manual|Contents]] | ||
[[Category:INCAR]][[Category:Electronic | [[Category:INCAR]][[Category:Electronic minimization]] | ||
Revision as of 12:53, 6 April 2022
KSPACING = [real]
Default: KSPACING = 0.5
Description: The tag KSPACING determines the number of k points if the KPOINTS file is not present.
KSPACING is the smallest allowed spacing between k points in units of [math]\displaystyle{ \AA^{-1} }[/math]. The number of k points increases when the spacing is decreased. The number of k points in the direction of the first, second and third reciprocal lattice vector is determined by [math]\displaystyle{ N= \mathrm{max}(1, | \vec{b}_i| / \mathrm{KSPACING} ). }[/math] These values are rounded to the next integer greater than or equal to [math]\displaystyle{ N }[/math]. In this equation, [math]\displaystyle{ \vec{b}_i }[/math] are the reciprocal lattice vectors [math]\displaystyle{ \vec{b}_i \vec{a}_j = 2 \pi \delta_{ij} }[/math]. The generated grid is either centred at the [math]\displaystyle{ \Gamma }[/math] point, i.e., includes the [math]\displaystyle{ \Gamma }[/math] point when (KGAMMA=.TRUE., or is shifted away from the [math]\displaystyle{ \Gamma }[/math] point, as done for Monkhorst-Pack grids when (KGAMMA=.FALSE.. The default is to include the [math]\displaystyle{ \Gamma }[/math] point.
| Warning: This implementation is not entirely consistent with the automatic k-point generation (Mode=A) used in the KPOINTS file. |
If the k points are generated using the automatic mode in the KPOINTS file, [math]\displaystyle{ N }[/math] is calculated as [math]\displaystyle{ N= \mathrm{max}(1, | \vec{b}_i| / (2 \pi \times \mathrm{KSPACING}) ) }[/math] and rounding is to the nearest integer. We recommend using the KSPACING tag in the INCAR file and avoiding the automatic mode via the KPOINTS file.