KSPACING: Difference between revisions
No edit summary |
No edit summary |
||
| Line 9: | Line 9: | ||
<math>\AA^{-1}</math>. The number of k-points increases when the spacing is decreased. | <math>\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 | 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} | reciprocal lattice vector is determined by <math> N= \mathrm{max}(1, | \vec{b}_i| / \mathrm{KSPACING} ). </math> | ||
These values are rounded to the next integer greater than or equal to <math> N </math>. In this equation | These values are rounded to the next integer greater than or equal to <math> N </math>. In this equation | ||
<math> \vec{b} | <math> \vec{b}_i </math> | ||
are the reciprocal lattice vectors <math> \vec{b} | 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 (e.g. includes the <math>\Gamma</math> point) ({{TAG|KGAMMA}}=''.TRUE.'') or is shifted away | The generated grid is either centred at the <math>\Gamma</math> point (e.g. includes the <math>\Gamma</math> point) ({{TAG|KGAMMA}}=''.TRUE.'') or is shifted away | ||
from the <math>\Gamma</math> point, as usually done for Monkhorst Pack grids ({{TAG|KGAMMA}}=''.FALSE.''). | from the <math>\Gamma</math> point, as usually done for Monkhorst Pack grids ({{TAG|KGAMMA}}=''.FALSE.''). | ||
The default is to include the <math>\Gamma</math> point. | |||
Note: 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> N</math> is calculated as | |||
<math> N= \mathrm{max}(1, | \vec{b}_i| / (2 \pi \times \mathrm{KSPACING}) ) </math> | |||
and rounding is to the nearest integer. We recommend to use the KSPACING tag in the INCAR file | |||
and to avoid using the automatic mode via the KPOINTS file. | |||
== Related Tags and Sections == | == Related Tags and Sections == | ||
Revision as of 09:30, 7 July 2017
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 . 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 These values are rounded to the next integer greater than or equal to . In this equation are the reciprocal lattice vectors . The generated grid is either centred at the point (e.g. includes the point) (KGAMMA=.TRUE.) or is shifted away from the point, as usually done for Monkhorst Pack grids (KGAMMA=.FALSE.). The default is to include the point.
Note: 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, is calculated as and rounding is to the nearest integer. We recommend to use the KSPACING tag in the INCAR file and to avoid using the automatic mode via the KPOINTS file.