KSPACING: Difference between revisions
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{{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. | {{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. | ||
The number of k points in the direction of the first, second and third reciprocal lattice vector is determined by <math> N_i= \mathrm{max}(1, \ | The number of k points in the direction of the first, second and third reciprocal lattice vector is determined by <math> N_i= \mathrm{max}(1, \mathrm{ceiling}( | \mathbf{b}_i| 2\pi / \mathrm{KSPACING} ))</math> | ||
with <math>\ | with <math>\mathrm{ceiling}( x )</math> being the ceiling function which returns the least integer that is equal or larger than <math>x</math>. In this equation, <math> \mathbf{b}_i </math> are the reciprocal lattice vectors <math> \mathbf{b}_i \mathbf{a}_j = \delta_{ij} </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. is set. The default is to include the <math>\Gamma</math> point. | 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. is set. The default is to include the <math>\Gamma</math> point. | ||
{{NB|warning|This implementation is not entirely consistent with the automatic k-point generation (Mode{{=}}A) used in the {{FILE|KPOINTS}} file.}} | {{NB|warning|This implementation is not entirely consistent with the automatic k-point generation (Mode{{=}}A) used in the {{FILE|KPOINTS}} file.}} | ||
Revision as of 18:45, 1 September 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 . 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 with being the ceiling function which returns the least integer that is equal or larger than . In this equation, are the reciprocal lattice vectors . The generated grid is either centred at the point, i.e., includes the point when KGAMMA=.TRUE., or is shifted away from the point, as done for Monkhorst-Pack grids when KGAMMA=.FALSE. is set. The default is to include the 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, is calculated as with and rounding it to the nearest integer. We recommend using the KSPACING tag in the INCAR file and avoiding the automatic mode via the KPOINTS file.