ODDONLY: Difference between revisions

Latest revision as of 12:04, 18 October 2023

ODDONLY = .TRUE. | .FALSE.
Default: ODDONLY = .FALSE.

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

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

{\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) }

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.

ODDONLY=.TRUE. selects a subset of k-points with C₁=C₂=C₃=1, and n₁+n₂+n₃ odd. 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).

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

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 {{TAG|ODDONLY}}=.TRUE. selects a subset of '''k'''-points with ''C''<sub>1</sub>=''C''<sub>2</sub>=''C''<sub>3</sub>=1, and ''n''<sub>1</sub>+''n''<sub>2</sub>+''n''<sub>3</sub> odd. 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''': [[Downsampling_of_the_Hartree-Fock_operator#Caveat: when one should not use downsampling|there are circumstances under which '''NKRED''' and '''NKREDX''','''Y''','''Z''' should not be used!]]
+{{NB|warning|[[Downsampling_of_the_Hartree-Fock_operator#Caveat: when one should not use downsampling|there are circumstances under which '''NKRED''' and '''NKREDX''','''Y''','''Z''' should not be used!]]}}
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