Recipe for GW 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, so that it might be better to perform the calculations in two steps: first a standard grounstate calculation with few unoccupied orbitals only,

System = Si groundstate occupied orbitals ISMEAR = 0 ; SIGMA = 0.05 ! small sigma is required to avoid partial occupancies EDIFF = 1E-8 ! required tight tolerance for groundstate orbitalsand second a calculation of a large number of unoccupied orbitals

System = Si unoccupied orbitals ALGO = Exact ! use exact diagonalization of the Hamiltonian NELM = 1 ! since we are already converged stop after one step NBANDS = 96 ISMEAR = 0 ; SIGMA = 0.05 ! small sigma is required to avoid partial occupancies LOPTICS = .TRUE.Furthermore note that the flag

System = Si NBANDS = 96 ISMEAR = 0 ; SIGMA = 0.05 LOPTICS = .TRUE. ALGO = GW0 ; NOMEGA = 50The head and wings of the dielectric matrix are constructed using k.p perturbation theory (this requires the file WAVEDER). In the present release the interaction between the core and the valence electrons is always treated on the Hartree Fock level [111].

For hybrid functionals, the three step procedure will accordingly involve the following INCAR files. In the first two steps, converged HSE03 orbitals are determined (usually HSE03 calculations should be preceeded by standard DFT calculations, we have not documented this step here, see Sec. 6.71.11):

System = Si groundstate occupied orbitals ISMEAR = 0 ; SIGMA = 0.05 ALGO = Damped ; TIME = 0.5 ! or ALGO = Conjugate LHFCALC = .TRUE. ; AEXX = 0.25 ; HFSCREEN = 0.3 EDIFF = 1E-6 ! required tight tolerance for groundstate orbitalsSecond determine the HSE03 orbitals for unoccupied states:

System = Si unoccupied orbitals NBANDS = 96 ALGO = Exact ! perform exact diagonalization NELM = 1 ! since we are already converged stop after one step ISMEAR = 0 ; SIGMA = 0.05 LHFCALC = .TRUE. ; AEXX = 0.25 ; HFSCREEN = 0.3 LOPTICS = .TRUE.As before, in the GW step, the head and the wings of the response matrix are determined by reading the required data from the WAVEDER file.

System = Si NBANDS = 96 ISMEAR = 0 ; SIGMA = 0.05 ALGO = GW0 ; NOMEGA = 50Convergence with respect to the number of empty bands