EVENONLY

EVENONLY = .TRUE. | .FALSE.
Default: EVENONLY = .FALSE. 

Description: EVENONLY=.TRUE. selects a subset of k-points for the representation of the Fock exchange potential, with C₁=C₂=C₃=1, and n₁+n₂+n₃ even.

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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

$\mathbf{q_k} = \mathbf{b}_1 \frac{n_1 C_1}{N_1} + \mathbf{b}_2 \frac{n_2 C_2}{N_2} + \mathbf{b}_3 \frac{n_3 C_3}{N_3},\quad(n_i=0,..,N_i-1)$

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.

EVENONLY=.TRUE. selects a subset of k-points with C₁=C₂=C₃=1, and n₁+n₂+n₃ even. It reduces the computational work load for HF type calculations by a factor two, but is only sensible for high symmetry cases (such as sc, fcc or bcc cells).

Mind: there are circumstances under which downsampling should not be used!

Related Tags and Sections

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

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