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Dear colleagues,
I am just starting to use VASP. I tested Si with 6x6x6 k-points and a0=5.43A with a primitive cell. The following INCAR setting is used for HSE06 iteration:

SYSTEM=Diamond-Si
ISTART=1
ENCUT=500
EDIFF=1.0E-6
NPAR=24
ICHARG=1
ISMEAR=0;SIGMA=0.01
GGA=PE
NSW=0
IBRION=-1
PREC=Accurate
PRECFOCK=Accurate
RWIGS=1.312
#LREAL=Auto
LWAVE=T
LCHARG=T
LHFCALC=.TRUE.;LFSCREEN=0.2;AEXX=0.25
ALGO=Damped; TIME=0.4; LDIAG=.TRUE.
NBANDS=24
NELMIN=5

After completiing computation, I then added 21 points from Gamma point to X point with zero weights to compute band structure.

In the output file EIGENVAL the energy levels at Gamma point appear two times, but they are different.
I also made two iterations with a slight difference in the setting in the INCAR file to check this. The following are energy levels at Gamma point for two iterations.

(1) the 1st time

0.0000000E+00 0.0000000E+00 0.0000000E+00 0.4629630E-02
1 -8.253518
2 5.135292
3 5.135292
4 5.135292
5 9.147447
6 9.147447
7 9.147447
8 10.158161
9 14.637926
10 14.652046
11 14.652046
12 18.198122
13 18.198122
14 18.198122
15 22.105391
16 30.649416
17 30.649416
18 30.649416
19 31.949594
20 31.949594
21 33.511650
22 33.511658
23 33.511658
24 36.681558


0.0000000E+00 0.0000000E+00 0.0000000E+00 0.0000000E+00
1 -8.253517
2 5.641836
3 5.641842
4 5.641837
5 9.147466
6 9.147446
7 9.147449
8 10.158160
9 14.652544
10 14.637926
11 14.652139
12 18.200481
13 18.198138
14 18.198637
15 22.107929
16 30.908348
17 30.925680
18 31.248338
19 32.203957
20 32.325096
21 33.690107
22 34.997818
23 37.239843
24 43.657886




(2) 2nd time
0.0000000E+00 0.0000000E+00 0.0000000E+00 0.4629630E-02
1 -8.253518
2 5.135292
3 5.135292
4 5.135292
5 9.147447
6 9.147447
7 9.147447
8 10.158161
9 14.637926
10 14.652046
11 14.652046
12 18.198122
13 18.198122
14 18.198122
15 22.105391
16 30.649416
17 30.649416
18 30.649416
19 31.949595
20 31.949595
21 33.511628
22 33.511628
23 33.511628
24 36.681558

0.0000000E+00 0.0000000E+00 0.0000000E+00 0.0000000E+00
1 -8.253518
2 5.135292
3 5.641827
4 5.641827
5 9.147447
6 9.147447
7 9.147447
8 10.158161
9 14.637926
10 14.652046
11 14.652046
12 18.198122
13 18.198122
14 18.198122
15 22.105391
16 30.649486
17 30.650178
18 30.650137
19 31.949939
20 31.952330
21 33.511824
22 33.520100
23 33.546944
24 39.000509

From above results, with a nonzero weight, the energy levels at the Gamma point are almost the same for two iterations.
Based on the vasp manual, it is known that with a non-zero weight, the enery levels are used for SCF iteration; and with non-zero weight, the energy levels
are not used for SCF iteration. My question is why for a nonzero weight, the energy levels are different from those with nonzero weight and depend on the specific iteration. In the second time, the top three valence bands at Gamma point are not degenerate anymore.
I also checked other K points. At the same k point, the energy levels with a zero weight are almost the same as those with a non-zero weight.

Can anyone help me to understand the reason? Thanks a lot

Paul

Dear all:

I rechecked my INCAR scprit. After initial PBE iteration, the first HSE06 iteration INCAR uses ISTART=1, ICHARG=0, the charge density is from inital orbitals. In the second HSE06 iteration INCAR uses ISTART=1, ICHARG=1, so the charge density is from CHGCAR. I feel
ISTART=1, ICHARG=0 should be better.



With the converged HSE06 WAVECAR, I contiue the HSE06 iteration by changing ALGO=N, so blocked Davidson iteration is used. This time
I have following energy levels at Gamma points from EIGENVAL:


0.0000000E+00 0.0000000E+00 0.0000000E+00 0.4629630E-02
1 -8.253622
2 5.135155
3 5.135158
4 5.135161
5 9.147400
6 9.147401
7 9.147402
8 10.158043
9 14.637642
10 14.651982
11 14.651982
12 18.198022
13 18.198026
14 18.198031
15 22.105039
16 30.649262
17 30.649269
18 30.649275
19 31.949496
20 31.949496
21 33.511471
22 33.511473
23 33.511475
24 36.681518


0.0000000E+00 0.0000000E+00 0.0000000E+00 0.0000000E+00
1 -8.253622
2 5.135155
3 5.135158
4 5.135161
5 9.147400
6 9.147401
7 9.147402
8 10.158043
9 14.637642
10 14.651982
11 14.651982
12 18.198022
13 18.198026
14 18.198031
15 22.105039
16 30.649262
17 30.649269
18 30.649275
19 31.949496
20 31.949496
21 33.511471
22 33.511473
23 33.511475
24 36.681519


The INCAR setting are:

SYSTEM=Diamond-Si
ISTART=1
ENCUT=500
EDIFF=1.0E-7
NPAR=24
ICHARG=0
ISMEAR=0;SIGMA=0.01
GGA=PE
NSW=0
IBRION=-1
PREC=Accurate
PRECFOCK=Accurate
RWIGS=1.312
#LREAL=Auto
LWAVE=T
LCHARG=T
LHFCALC=.TRUE.;LFSCREEN=0.2;AEXX=0.25
#ALGO=Damped; TIME=0.4; LDIAG=.TRUE.
ALGO=N; LDIAG=.TRUE.
NBANDS=24
NELMIN=10



The energy levels at other K points are not given here. This time two sets of energy levels at GAMMA points are almost the same. However, indirect bad gap is 1.82 eV. In comparison, from energy levels of K points with zero weights and ALGO=damped, TIME=0.4, the indrect band gap is 1.3 eV.
I use VASP .5.2.12. Kpoints are still 6x6x6. Both POSCAR (a0=5.43A) and POTCAR are fixed.

Can anyone help me to explain the results? very thankful!


Paul