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# NKREDX

NKREDX = [integer]

Default: **NKREDX** = 1

Description: NKREDX specifies a reduction factor for the **q**-point grid representation of the exact exchange potential along reciprocal space direction **b**_{1}.

One may restrict the sum over **q** in the Fock exchange potential (or one of its short range counterparts) to a subset, {**q**_{k}}, of the full (*N*_{1}×*N*_{2}×*N*_{3}) **k**-point set, {**k**}, for which the following holds

where **b**_{1,2,3} are the reciprocal lattice vectors of the primitive cell,
and *C*_{i} is the integer grid reduction factor along reciprocal lattice direction
**b**_{i}. This leads to a reduction in the computational workload by a factor:

In case one sets NKRED, the grid reduction factors will be uniformly set to *C*_{1}=*C*_{2}=*C*_{3}=NKRED. If one wants to specify separate grid reduction factors for *C*_{1}, *C*_{2}, and *C*_{3} one should use *C*_{1}=NKREDX, *C*_{2}=NKREDY, and *C*_{3}=NKREDZ, respectively.

**Mind**: there are circumstances under which **NKRED** and **NKREDX**,**Y**,**Z** should not be used!

## Related Tags and Sections

NKRED, NKREDY, NKREDZ, EVENONLY, ODDONLY, downsampling, Hartree-Fock_and_HF/DFT_hybrid_functionals