ENCUTFOCK = [real]
Description: The ENCUTFOCK tag sets the energy cutoff that determines the FFT grids used by the Hartree-Fock routines.
The only sensible value for ENCUTFOCK is ENCUTFOCK=0. This implies that the smallest possible FFT grid, which just encloses the cutoff sphere corresponding to the plane wave cutoff, is used. This accelerates the calculations by roughly a factor two to three, but causes slight changes in the total energies and some noise in the calculated forces. The FFT grid used internally in the exact exchange (Hartree-Fock) routines is written to the OUTCAR file. Simply search for lines starting with
FFT grid for exact exchange (Hartree Fock)