Recipy for G$_0$W$_0$ calculations

GW calculations always require the calculation of a standard DFT WAVECAR file in an initial step, using for instance the following INCAR file:

 System  = Si
 NBANDS = 96
 ISMEAR = 0 ; SIGMA = 0.05  ! small sigma is required to avoid partial occupancies
 LOPTICS = .TRUE.

Note, that the a significant number of empty bands is required for GW calculations. Furthermore note that the flag LOPTICS=.TRUE. is required in order to write the file WAVEDER, which contains the derivative of the wavefunctions with respect to k. The actual GW calculations are performed in a second step, using an INCAR file such as (it is convenient to add a single line):

 System  = Si
 NBANDS = 96
 ISMEAR = 0 ; SIGMA = 0.05
 LOPTICS = .TRUE.
 ALGO = GW0 ; NOMEGA = 50

The head and wings of the dielectric matrix are constructed using k.p perturbation theory (this requires that the file WAVEDER exists). In the present release the interaction between the core and the valence electrons is always treated on the Hartree Fock level.

For hybride functionals, the two step procedure will accordingly involve the following INCAR files. In the first step, converged HSE03 wave functions are determined (usually HSE03 calculations should be preceeded by standard DFT calculations, we have not documented this step here, see Sec. 6.64.10):

 System  = Si
 NBANDS = 96
 ISMEAR = 0 ; SIGMA = 0.05
 ALGO = Damped ; TIME = 0.5 
 LHFCALC = .TRUE. ; AEXX = 0.25 ; HFSCREEN = 0.3 
 LOPTICS = .TRUE.

In the GW step, the head and the wings of the response matrix are correctly determined by reading the required data from the WAVEDER file.

 System  = Si
 NBANDS = 96
 ISMEAR = 0 ; SIGMA = 0.05
 ALGO = GW0 ; NOMEGA = 50

Convergence with respect to the number of empty bands NBANDS and with respect to the number of frequencies NOMEGA must be checked carfully.