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# 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 *C*_{1}=*C*_{2}=*C*_{3}=1, and *n*_{1}+*n*_{2}+*n*_{3} even.

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}.

EVENONLY=.TRUE. selects a subset of **k**-points with *C*_{1}=*C*_{2}=*C*_{3}=1, and *n*_{1}+*n*_{2}+*n*_{3} 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