NKRED: Difference between revisions
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Description: {{TAG|NKRED}} specifies an uniform reduction factor for the '''q'''-point grid representation of the exact exchange potential and the correlation part in GW calculations. | Description: {{TAG|NKRED}} specifies an uniform reduction factor for the '''q'''-point grid representation of the exact exchange potential and the correlation part in GW calculations. | ||
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One may restrict the sum over '''q''' in the [[ | One may restrict the sum over '''q''' in the [[Hybrid functionals: formalism|Fock exchange potential]] (or one of its short range counterparts) to a subset, {'''q'''<sub>'''k'''</sub>}, of the full (''N''<sub>1</sub>×''N''<sub>2</sub>×''N''<sub>3</sub>) '''k'''-point set, {'''k'''}, for which the following holds | ||
:<math> | :<math> | ||
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is reduced to a subgrid specified by the {{TAG|NKRED}} parameters. | is reduced to a subgrid specified by the {{TAG|NKRED}} parameters. | ||
{{NB|warning|[[Downsampling_of_the_Hartree-Fock_operator#Caveat: when one should not use downsampling|there are circumstances under which '''NKRED''' and '''NKREDX''','''Y''','''Z''' should not be used!]]}} | |||
== Related tags and articles == | == Related tags and articles == | ||
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[[Category:INCAR tag]][[Category:Exchange-correlation functionals]][[Category:Hybrid_functionals]][[Category:Many- | [[Category:INCAR tag]][[Category:Exchange-correlation functionals]][[Category:Hybrid_functionals]][[Category:Many-body perturbation theory]][[Category:GW]] | ||
Latest revision as of 12:03, 18 October 2023
NKRED = [integer]
Default: NKRED = 1
Description: NKRED specifies an uniform reduction factor for the q-point grid representation of the exact exchange potential and the correlation part in GW calculations.
One may restrict the sum over q in the Fock exchange potential (or one of its short range counterparts) to a subset, {qk}, of the full (N1×N2×N3) k-point set, {k}, for which the following holds
- [math]\displaystyle{ \mathbf{q_k} = \mathbf{b}_1 \frac{n_1 C_1}{N_1} + \mathbf{b}_2 \frac{n_2 C_2}{N_2} + \mathbf{b}_3 \frac{n_3 C_3}{N_3},\quad(n_i=0,..,N_i-1) }[/math]
where b1,2,3 are the reciprocal lattice vectors of the primitive cell, and Ci is the integer grid reduction factor along reciprocal lattice direction bi. This leads to a reduction in the computational workload by a factor:
- [math]\displaystyle{ \frac{1}{C_1 C_2 C_3} }[/math]
In case one sets NKRED, the grid reduction factors will be uniformly set to C1=C2=C3=NKRED. If one wants to specify separate grid reduction factors for C1, C2, and C3 one should use C1=NKREDX, C2=NKREDY, and C3=NKREDZ, respectively.
This flag also applies to GW and RPA calculations with a similar speedup. In GW and RPA type calculations, analogously to hybrid functional calculations the outermost loop over the momentum transfer q is reduced to a subgrid specified by the NKRED parameters.
| Warning: there are circumstances under which NKRED and NKREDX,Y,Z should not be used! |
Related tags and articles
NKREDX, NKREDY, NKREDZ, EVENONLY, ODDONLY, downsampling