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 b₁.

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 (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 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:

[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.

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

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