** Next:** Optical properties and density
** Up:** Hartree-Fock (HF) type and
** Previous:** When NKRED should not
** Contents**
** Index**

*N.B. This document is no longer maintained, please visit our wiki.*
###

Typical hybrid functional and Hartree-Fock calculations

It is strongly recommended to perform standard DFT calculations
first, and to start Hartree-Fock type calculations from a preconverged WAVECAR file.

A typical INCAR file for a Hartree-Fock or hybrid HF/DFT calculation for an
insulator or semiconductor has the following input lines:

ISTART = 1
LHFCALC = .TRUE. ; HFSCREEN = 0.2
NBANDS = number of occupied bands
ALGO = All ; TIME = 0.4
PRECFOCK = Fast ! used PRECFOCK = Normal for high quality calculations
NKRED = 2 ! omit flag for high quality calculations

For metals and small gap semiconductors it is recommended to use.
ISTART = 1
LHFCALC = .TRUE. ; HFSCREEN = 0.2
ALGO = Damped ; TIME = 0.4
PRECFOCK = Fast ! used PRECFOCK = Normal for high quality calculations
NKRED = 2 ! omit flag for high quality calculations

These input files select the HSE06 functional, which tends to yield very
similar thermochemistry as the PBE0 functional, but converges more rapidly
with respect to the number of k-points [99]. We thus recommend to
apply and use this functional instead of the more demanding PBE0 functional.
The `NKRED` flag is applicable, if and only if the number of k-points is
dividable by `NKRED` (see Sec. 6.71.9). `PRECFOCK= fast` selects
a smaller FFT grid for the fast-Fourier-transforms (see Sec. 6.71.5).
For high accuracy `NKRED` and in particular `PRECFOCK= fast` should be ommited, but
we recommend to do this only after preconverging the orbitals and
atomic positions with the flags specified above.
Mind, that the parameter `TIME` defaults to 0.4, and
for the present algorithm this hardly ever needs to be changed.
If divergence is observed, simply decrease `TIME` until the
damped or conjugate gradient algorithm become stable (see Sec. 6.47
and 6.51).

Standard Hartree-Fock type calculations require one to set the flag `AEXX = 1.0`
to switch on full non-local exchange (local exchange and correlation are
automatically switched off):

ISTART = 1
LHFCALC = .TRUE. ; AEXX = 1.0 ;
NBANDS = number of occupied bands
ALGO = All ; TIME = 0.4
PRECFOCK = Fast ! used PRECFOCK = Normal for high quality calculations
NKRED = 2 ! omit flag for high quality calculations

Concerning `NKRED` and `PRECFOCK` the same considerations
as above apply. Matter of fact, it is also possible to try
to converge using the ``metallic'' setup given above.

N.B. Requests for support are to be addressed to: vasp.materialphysik@univie.ac.at