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Bandgap issue
Date: 2022/05/04 15:48
Name: Wei Li   <liwei0099@gmail.com>

Dear Developers,

We have recently computed the bandgap of CsPbI3 perovskite with 2x2x2 supercell using openmx.
The reference PBE bandgap is about 1.6 eV at Gamma, SOC gap is about 0.6 eV.

We obtained the bandgap by looking into either out file of openmx scf calculation or diagonalizing the H with transformation matrix.
We found the obtained PBE/GGA bandgap is about 1.4 eV, which is 0.2-0.3 eV smaller than the reference value.

We also found after applying SOC, the bandgap decreases to about 0.01 eV, still much smaller than the reference value.

Any ideas to improve the openmx band gap?

below is the input file I used.

many thanks.

Wei


# This was generated by OpenMX Viewer

System.CurrrentDirectory ./
System.Name x0
level.of.stdout 3
level.of.fileout 3
HS.fileout on

Species.Number 3
<Definition.of.Atomic.Species
I I7.0-s3p2d2f1 I_PBE19
Cs Cs12.0-s3p2d2 Cs_PBE19
Pb Pb8.0-s3p2d2f1 Pb_PBE19
Definition.of.Atomic.Species>


Atoms.Number 40
Atoms.SpeciesAndCoordinates.Unit Ang
<Atoms.SpeciesAndCoordinates
1 Cs 3.2070725 3.2070725 3.2070725 4.5 4.5
2 Cs 3.2070725 3.2070725 9.6212175 4.5 4.5
3 Cs 3.2070725 9.6212175 3.2070725 4.5 4.5
4 Cs 3.2070725 9.6212175 9.6212175 4.5 4.5
5 Cs 9.6212175 3.2070725 3.2070725 4.5 4.5
6 Cs 9.6212175 3.2070725 9.6212175 4.5 4.5
7 Cs 9.6212175 9.6212175 3.2070725 4.5 4.5
8 Cs 9.6212175 9.6212175 9.6212175 4.5 4.5
9 Pb 0.0000000 0.0000000 0.0000000 7.0 7.0
10 Pb 0.0000000 0.0000000 6.4141450 7.0 7.0
11 Pb 0.0000000 6.4141450 0.0000000 7.0 7.0
12 Pb 0.0000000 6.4141450 6.4141450 7.0 7.0
13 Pb 6.4141450 0.0000000 0.0000000 7.0 7.0
14 Pb 6.4141450 0.0000000 6.4141450 7.0 7.0
15 Pb 6.4141450 6.4141450 0.0000000 7.0 7.0
16 Pb 6.4141450 6.4141450 6.4141450 7.0 7.0
17 I 0.0000000 0.0000000 3.2070725 3.5 3.5
18 I 0.0000000 0.0000000 9.6212175 3.5 3.5
19 I 0.0000000 6.4141450 3.2070725 3.5 3.5
20 I 0.0000000 6.4141450 9.6212175 3.5 3.5
21 I 6.4141450 0.0000000 3.2070725 3.5 3.5
22 I 6.4141450 0.0000000 9.6212175 3.5 3.5
23 I 6.4141450 6.4141450 3.2070725 3.5 3.5
24 I 6.4141450 6.4141450 9.6212175 3.5 3.5
25 I 0.0000000 3.2070725 0.0000000 3.5 3.5
26 I 0.0000000 3.2070725 6.4141450 3.5 3.5
27 I 0.0000000 9.6212175 0.0000000 3.5 3.5
28 I 0.0000000 9.6212175 6.4141450 3.5 3.5
29 I 6.4141450 3.2070725 0.0000000 3.5 3.5
30 I 6.4141450 3.2070725 6.4141450 3.5 3.5
31 I 6.4141450 9.6212175 0.0000000 3.5 3.5
32 I 6.4141450 9.6212175 6.4141450 3.5 3.5
33 I 3.2070725 0.0000000 0.0000000 3.5 3.5
34 I 3.2070725 0.0000000 6.4141450 3.5 3.5
35 I 3.2070725 6.4141450 0.0000000 3.5 3.5
36 I 3.2070725 6.4141450 6.4141450 3.5 3.5
37 I 9.6212175 0.0000000 0.0000000 3.5 3.5
38 I 9.6212175 0.0000000 6.4141450 3.5 3.5
39 I 9.6212175 6.4141450 0.0000000 3.5 3.5
40 I 9.6212175 6.4141450 6.4141450 3.5 3.5
Atoms.SpeciesAndCoordinates>

Atoms.UnitVectors.Unit Ang
<Atoms.UnitVectors
12.8282900 0.0000000 0.0000000
0.0000000 12.8282900 0.0000000
0.0000000 0.0000000 12.8282900
Atoms.UnitVectors>

scf.XcType GGA-PBE
scf.SpinPolarization NC
scf.SpinOrbit.Coupling on
scf.ElectronicTemperature 300.0
scf.energycutoff 220.0
scf.maxIter 100
scf.EigenvalueSolver band
scf.Kgrid 1 1 1
scf.Mixing.Type rmm-diisk
scf.Init.Mixing.Weight 0.05
scf.Min.Mixing.Weight 0.01
scf.Max.Mixing.Weight 0.30
scf.Mixing.History 25
scf.Mixing.StartPulay 15
scf.criterion 1.0e-7

#MD.Type nomd
#MD.maxIter 1
#MD.TimeStep 1.0
#MD.Opt.criterion 0.0003

MO.fileout on # on|off
num.HOMOs 1 # default=1
num.LUMOs 1 # default=1
MO.Nkpoint 1 # default=1
<MO.kpoint
0.0 0.0 0.0
MO.kpoint>

Dos.fileout on # on|off , default=off
Dos.Erange -10.0 10.0 # default = -20 20
#Dos.Kgrid 1 1 1 # default = Kgrid1 Kgrid2 Kgrid3
メンテ
Page: [1]

Re: Bandgap issue ( No.1 )
Date: 2022/05/08 07:15
Name: Wei Li  <liwei0099@gmail.com>

PS.
メンテ
Re: Bandgap issue ( No.2 )
Date: 2022/05/08 07:14
Name: Wei Li  <liwei0099@gmail.com>

Dear Developers,

For polB.c script, not sure why we have fsize3=fsize+2 (SpinP_switch==0) or fsize3=2*fsize+2 (SpinP_switch==3).
fsize is the number of AO basis. But why there is +2 for fsize3?

Thanks in advance!

Wei

メンテ
Re: Bandgap issue ( No.3 )
Date: 2022/05/08 20:23
Name: Naoya Yamaguchi

Dear Wei,

The `+2` for `fsize3` was a treatment to begin the array index from 1 instead of 0, and it is not related to the physical meaning.

Regards,
Naoya Yamaguchi
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