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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

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:

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.

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

Related Tags and Sections

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

Examples that use this tag