next up previous contents index
Next: Optical properties and density Up: Hartree-Fock (HF) type and Previous: When NKRED should not   Contents   Index


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.


next up previous contents index
Next: Optical properties and density Up: Hartree-Fock (HF) type and Previous: When NKRED should not   Contents   Index
N.B. Requests for support are to be addressed to: vasp.materialphysik@univie.ac.at