formation energy of Si diamond is not consistent with VASP |
- Date: 2022/06/12 23:05
- Name: IK
- The formation energy is about -4.55 eV/atoms when calculated with VASP, but with OpenMX it is -5.66 eV/atoms, a discrepancy of about 1.1 eV/atoms.
Similarly, when the cell is scaled larger or smaller (E-V curve), the difference is about 1.1 eV/atoms.
Why does this happen? I would appreciate it if you could tell me if my calculation conditions are wrong.
The main calculation conditions are as follows. For single Si atom:
DATA.PATH ../DFT_DATA19/
Species.Number 1
<Definition.of.Atomic.Species
Si Si7.0-s2p2d1 Si_PBE19
Definition.of.Atomic.Species>
Atoms.SpeciesAndCoordinates.Unit Ang
<Atoms.SpeciesAndCoordinates
1 Si 0.0 0.0 0.0 2.0 2.0
Atoms.SpeciesAndCoordinates>
Atoms.UnitVectors.Unit Ang
<Atoms.UnitVectors
14.001 0.0 0.0
0.0 13.999 0.0
0.0 0.0 14.0
Atoms.UnitVectors>
scf.Kgrid 22 22 22
scf.ElectronicTemperature 300
scf.energycutoff 200
scf.criterion 1e-07
scf.XcType GGA-PBE
scf.EigenvalueSolver band
scf.Mixing.Type rmm-diisk
scf.Hubbard.U Off
scf.SpinPolarization off
and the result is -106.1364 eV. For the bulk Si diamond, the following parts are different The result is -894.4000 eV
<Atoms.SpeciesAndCoordinates
1 Si 0.0 2.73477243 0.0 2.0 2.0
2 Si 1.367386215 4.102158645 1.367386215 2.0 2.0
3 Si 0.0 0.0 2.73477243 2.0 2.0
4 Si 1.367386215 1.367386215 4.102158645 2.0 2.0
5 Si 2.73477243 2.73477243 2.73477243 2.0 2.0
6 Si 4.102158645 4.102158645 4.102158645 2.0 2.0
7 Si 2.73477243 0.0 0.0 2.0 2.0
8 Si 4.102158645 1.367386215 1.367386215 2.0 2.0
Atoms.SpeciesAndCoordinates>
<Atoms.UnitVectors
5.46954486 0.0 0.0
0.0 5.46954486 0.0
0.0 0.0 5.46954486
Atoms.UnitVectors>
scf.Kgrid 11 11 11
The bulk Si diamond structure was obtained by structure optimization with VASP.
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Re: formation energy of Si diamond is not consistent with VASP