Bandgap problems of bulk GaAs using G0W0

[Ken-Ming Lin]

Dear All,

I am running the G0W0 for the bulk GaAs by VASP 5.3.3 and try to reproduce the results of M. Shishkin and G. Kresse, Phys. Rev. B 74, 035101 (2006). I used three steps as the VASP guide and the same parameters of the paper except NBANDS (e.g., I used NBANDS=168 and those of paper PRB 74, 035101 is 160.). However, I can not get the same results. My procedures are as follows,

1. The standard groundstate calculation with few unoccupied orbitals only.

INCAR
System = Bulk GaAs GS occupied orbitals (From VASP Guide p133)
ISMEAR = 0; SIGMA = 0.05
EDIFF = 1E-8
ENCUT = 310

POSCAR
GaAs_Bulk
5.650000000
0.00000000 0.50000000 0.50000000
0.50000000 0.00000000 0.50000000
0.50000000 0.50000000 0.00000000
1 1
Direct
-0.1250000 -0.1250000 -0.1250000
0.1250000 0.1250000 0.1250000

KPOINTS
6x6x6
0
G
6 6 6
0 0 0

POTCAR
PAW Ga_d_GW 06Jul2010
PAW As_GW 12Mar2012

2. The second calculation of a large number of unoccupied orbitals. After the first step calculation was finished, I copied all the files to a new empty directory and replaced the INCAR as follows,

INCAR
System = Bulk GaAs GS occupied orbitals (From VASP Guide p133)
ALGO = Exact
NELM = 1
NBANDS = 168 ! The NBANDS of paper PRB74, 035101 is 160.
ISMEAR = 0; SIGMA = 0.05
LOPTICS = .TRUE.
ENCUT = 310

3. After the second step calculation was finished, I copied all the files to another new empty directory and replaced the following INCAR to perform G0W0 calculation.

INCAR
System = Bulk GaAs G0W0 Phys. Rev. B 74, 035101 (2006)
ALGO = GW0; NOMEGA = 300
NBANDS = 168
ISMEAR = 0; SIGMA = 0.05
LOPTICS = .TRUE.
ENCUT = 310
CSHIFT = 0.1
ENCUTGW = 250

My results for Gamma point are as follows,
k-point 1 : 0.0000 0.0000 0.0000
band No./ KS-energies/ QP-energies/ Ga-3d_LDA[1]/ Ga-3d_GW[1]
5/ -14.947/ -16.552/ -14.94/ -13.61
6/ -12.779/ -12.621/ -12.79/ -12.76
9/ 0.00/ 0.00/ 0.00/ 0.00
10/ 0.337/ 1.229/ 0.31/ 1.42
13/ 3.669/ 4.171/ 3.65/ 4.40
[1] PRB 74, 035101 (2006).

The energies of the second and third columns are my results. The fourth and fifth columns are from the TABLE III in the paper PRB 74, 035101. All my energies are refered to the energy of band no. 9. My KS-energy are almost the same with those of the paper. Nevertheless, the QP-energy are different. Does any body have suggestions?



Thanks,

Ken-Ming Lin

[giacomo giorgi]

Hi,
what about using
ICHARG=11
in step 2?
As far as I know indeed the second step should be NSCF.
Anyway, I don't know if this will fix your problem.

Cheers,
Giacomo