GW calculation
with VASP
Giyeol Bae
10
Energy (eV)
5
0
-5
-10
L
G
X
U
G
K
(0.42, 0.42, 0)
6
5
k
4
Energy (eV)
3
2
1
0
Eg = 0.61 eV
-1
-2
-3
-4
<Solid State Electronic Devices,
6th Ed, Ben G. Streetman>
L
G
X
U
k
K
G
GW0 calculations
+ CHGCAR, WAVECAR
+ CHGCAR, WAVECAR, WAVEDER
200
5
• From VASP version of 5.2.XX, the interaction between the core and
the valence electrons is always treated on the Hartree Fock level.
VBM
KPTS : 7X7X7
CBM
Iteration
• EQP of Band 4 at k-point (0, 0, 0) -VBM
5.6364 → 6.5290 → 6.7200 → 6.7635 → 6.7740 → 6.7765
• EQP of Band 5 at k-point (0.4286, 0.4286, 0) -CBM
6.2512 → 7.5355 → 7.7997 → 7.8532 → 7.8645 → 7.8670
• Bandgap
0.6148 → 1.0065 → 1.0797 → 1.0897 → 1.0905 → 1.0905
Iteration(NOMEGA=50)
• EQP of Band 16 at k-point (0, 0, 0) -VBM
5.6364 → 6.5274 → 6.7222 → 6.7663 → 6.7767 → 6.7793
• EQP of Band 17 at k-point (0.4286, 0.4286, 0) -CBM
6.2512 → 7.5420 → 7.8155 → 7.8714 → 7.8832 → 7.8858
• Bandgap
0.6148 → 1.0146 → 1.0933 → 1.1051 → 1.1065 → 1.1065
NOMEGA = [integer]
- NOMEGA specifies the number of frequency grid points.
- For quick and memory conserving calculations, NOMEGA=20-30 can be used but it may
make errors of the order of 20-50 meV for the gap, and 100-200 meV for CBM.
- NOMEGA=30 is usually only slightly faster than NOMEGA=100-200.
Iteration(NOMEGA=300)
• EQP of Band 16 at k-point (0, 0, 0) -VBM
5.6364 → 6.5140 → 6.6961 → 6.7391 → 6.7495 → 6.7521
• EQP of Band 17 at k-point (0.4286, 0.4286, 0) -CBM
6.2512 → 7.5259 → 7.7882 → 7.8418 → 7.8531 → 7.8557
• Bandgap
0.6148 → 1.0119 → 1.0921 → 1.1027 → 1.1036 → 1.1036
NOMEGA = [integer]
- NOMEGA specifies the number of frequency grid points.
- Too large values for NOMEGA in combination with coarse k-point grids can
cause a decrease in precision.
Iteration(ENCUTGW=250)
• EQP of Band 16 at k-point (0, 0, 0) -VBM
5.6364 → 6.5266 → 6.7172 → 6.7607 → 6.7711 → 6.7737
• EQP of Band 17 at k-point (0.4286, 0.4286, 0) -CBM
6.2512 → 7.5346 → 7.7987 → 7.8521 → 7.8634 → 7.8660
• Bandgap
0.6148 → 1.0080 → 1.0815 → 1.0914 → 1.0923 → 1.0923
ENCUTGW = [real] (default value doesn’t set to ENCUT, must be set manually)
- ENCUTGW controls the basis set for the response functions in exactly the
same manner as ENCUT.
- Choosing ENCUTGW=ENCUT yields essentially exact results..
Recommended to omit for high quality calculation.
• ODDONLYGW = .TRUE. | .FALSE.(default)
EVENONLYGW = .TRUE. | .FALSE.(default)
- ODDONLYGW allows to avoid the inclusion of the Γ-point in the evaluation
of response functions.
- If the Γ-point is included, convergence is very slow for some materials.
• NKRED = [integer], NKREDX = [integer], NKREDY = [integer],
NKREDZ = [integer]
- NKRED, or alternatively, NKREDX, NKREDY, and NKREDZ are the grid
reduction factors that may be used to evaluate the Hartree-Fock kernel at a
subgrid of q-points.
4
(0.16, 0, 0)
Energy (eV)
2
0
Eg = 0.58 eV
-2
-4
Γ
Χ
Μ
k
R
Γ
VBM
CBM
KPTS : 6X6X6
Iteration (NBANDS = 64)
• EQP of Band 16 at k-point (0, 0, 0) -VBM
5.6462 → 5.9145 → 5.9993 → 6.0220 → 6.0278 → 6.0294
• EQP of Band 17 at k-point (0.1667, 0, 0) -CBM
6.2582 → 6.8867 → 7.0183 → 7.0471 → 7.0537 → 7.0552
• Bandgap
0.6120 → 0.9722 → 1.0190 → 1.0251 → 1.0259 → 1.0258
Iteration (NBANDS = 96)
• EQP of Band 16 at k-point (0, 0, 0) -VBM
5.6462 → 5.7116 → 5.7514 → 5.7634 → 5.7666 → 5.7674
• EQP of Band 17 at k-point (0.1667, 0, 0) -CBM
6.2582 → 6.7150 → 6.8045 → 6.8233 → 6.8274 → 6.8283
• Bandgap
0.6120 → 1.0034 → 1.0531 → 1.0599 → 1.0608 → 1.0609
Iteration (NBANDS = 128)
• EQP of Band 16 at k-point (0, 0, 0) -VBM
5.6462 → 5.5234 → 5.5238 → 5.5266 → 5.5276 → 5.5279
• EQP of Band 17 at k-point (0.1667, 0, 0) -VBM
6.2582 → 6.5653 → 6.6197 → 6.6301 → 6.6322 → 6.6327
• Bandgap
0.6120 → 1.0419 → 1.0959 → 1.1035 → 1.1046 → 1.1048
Iteration (NOMEGA = 300)
• EQP of Band 16 at k-point (0, 0, 0) -VBM
5.6462 → 6.7589 → 6.9489 → 6.9858 → 6.9938 → 6.9957
• EQP of Band 17 at k-point (0.1667, 0, 0) -CBM
6.2582 → 7.9815 → 8.2954 → 8.3481 → 8.3577 → 8.3595
• Bandgap
0.6120 → 1.2226 → 1.3465 → 1.3623 → 1.3639 → 1.3638
NOMEGA = [integer]
- NOMEGA specifies the number of frequency grid points.
- Too large values for NOMEGA in combination with coarse k-point grids can
cause a decrease in precision.
Setting PRECFOCK to ‘Fast’ saves time considerably for small systems without harm in accuracy.
PRECFOCK = Fast | Normal(default) | Accurate | Low | Medium
(M&L cause significant noise in the forces and are no longer recommended)
- PRECFOCK determines the FFT grid in all GW (and Hartree-Fock) related
routines..
- For small systems (which are often dominated by FFT operations), it can have a
significant impact on the compute time for QP calculations.
- For large systems, the FFT usually do not dominating the computational work
load.
- QP shifts are usually not very sensitive to the setting of PRECFOCK.