NKRED
NKRED = [integer]
Default: NKRED = 1
Description: NKRED specifies an uniform reduction factor for the q-point grid representation of the exact exchange potential.
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 (N 1×N 2×N 3) 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 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 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: [[Hartree-Fock_and_HF/DFT_hybrid_functionals#downsampling|there are circumstances under which NKRED should not be used]].
Related Tags and Sections
NKREDX, NKREDY, NKREDZ, EVENONLY, ODDONLY, downsampling, Hartree-Fock_and_HF/DFT_hybrid_functionals