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SiC polymorphic DOS does not match with VASP
Date: 2022/08/22 11:27
Name: IK

For the "Computed" cif of the SiC polymorphs listed in the Materials project at https://materialsproject.org/materials/mp-624397 , VASP (Materials project) shows it as an insulator while OpenMX shows a metal. The input of OpenMX is shown below. 0.03 eV Gaussian broadening was used for DosMain.

System.CurrentDirectory ./
System.Name tmp
DATA.PATH /opt/openmx3.9/DFT_DATA19
level.of.fileout 1
Species.Number 2
<Definition.of.Atomic.Species
Si Si7.0-s2p2d1 Si_PBE19
C C6.0-s2p2d1 C_PBE19
Definition.of.Atomic.Species>
Atoms.Number 22
Atoms.SpeciesAndCoordinates.Unit Ang
<Atoms.SpeciesAndCoordinates
1 Si 75.6039805720998 4.213848543174069 2.437905328148616 2.0 2.0
2 Si 30.24353821516888 1.6856478783796807 0.9752248810036259 2.0 2.0
3 Si 15.124305542756785 0.842965309440123 0.48769422969828613 2.0 2.0
4 Si 45.362438240345256 2.528311906958545 1.462744805856969 2.0 2.0
5 Si 35.28497339608781 1.9666363148597217 1.1377896242363879 2.0 2.0
6 Si 50.405120848398134 2.8093698697911846 1.625349773284718 2.0 2.0
7 Si 0.002411692458953003 0.0001344176150229486 7.776677697453233e-05 2.0 2.0
8 Si 68.04390684594468 3.792481765708338 2.194125253624451 2.0 2.0
9 Si 25.201936710632094 1.404650171719293 0.8126547745448656 2.0 2.0
10 Si 60.483749957980585 3.3711103531524325 1.950342497487287 2.0 2.0
11 Si 10.081872420130706 0.5619212518780037 0.32509730710953466 2.0 2.0
12 C 66.14499010085044 3.6866441166933717 2.1328933024025036 2.0 2.0
13 C 8.188028545381163 0.4563663433636034 0.2640289342805338 2.0 2.0
14 C 73.7050638270056 4.108010894159103 2.376673376926669 2.0 2.0
15 C 13.231043800669749 0.7374428465569351 0.4266446281602791 2.0 2.0
16 C 23.30842548311827 1.2991138035655858 0.7515971281678613 2.0 2.0
17 C 28.351523900215785 1.5801949418490908 0.9142155036606057 2.0 2.0
18 C 58.58483321288636 3.265272704137468 1.8891105462653395 2.0 2.0
19 C 48.51152645907538 2.703828866547304 1.5642894452947147 2.0 2.0
20 C 81.26497122954287 4.529368401444488 2.6204480882248355 2.0 2.0
21 C 33.39137900676506 1.861095311615841 1.0767292962463844 2.0 2.0
22 C 43.468927012831436 2.422775538804838 1.4016871594799647 2.0 2.0
Atoms.SpeciesAndCoordinates>
Atoms.UnitVectors.Unit Ang
<Atoms.UnitVectors
27.8355398 0.0 0.0
27.663134295508943 3.0932631485246675 0.0
27.663134833904955 1.5418270246804564 2.6816129991218047
Atoms.UnitVectors>
scf.Kgrid 8 8 8
scf.maxIter 100
scf.Mixing.History 25
scf.Mixing.StartPulay 15
scf.ElectronicTemperature 300
scf.energycutoff 200
scf.Init.Mixing.Weight 0.05
scf.Min.Mixing.Weight 0.01
scf.Max.Mixing.Weight 0.3
scf.criterion 4e-08
scf.XcType GGA-PBE
scf.EigenvalueSolver band
scf.Mixing.Type rmm-diisk
scf.Hubbard.U Off
scf.stress.tensor On
level.of.stdout 1
HS.fileout On
scf.SpinPolarization off
Dos.fileout on
Dos.Erange -10.0 10.0
Dos.Kgrid 16 16 16

To improve the accuracy of OpenMX, I varied the cutoff energy from 200->300->400->500 and used s3p3d2 instead of s2p2d1, but the qualitative results did not change. In all cases, the SCF itself converged.
Is there anything else I should change in the calculation conditions?
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Re: SiC polymorphic DOS does not match with VASP ( No.1 )
Date: 2022/08/24 14:11
Name: T. Ozaki

Hi,

For such a slimline unit cell with very sharp angles between unit cell vectors, the convergence of the numerical integration
by the regular mesh tends to be quite slow. To check the convergence, I increased scf.energycutoff to 2000 Ryd., and got
a proper gap of ~ 2 eV, being comparable to that shown at https://materialsproject.org/materials/mp-624397

On the other hand, for the conventional cell including 66 atoms, it turned out that the scf.energycutof of 220 Ryd. is enough
to get the proper gap, which implies that the convergence for scf.energycutof strongly depends on the shape of the unit cell.

So, I wonder that this is a good example reminding us that we need to be careful when a slimline unit cell with very
sharp angles is treated.

Regards,

TO
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