[Pw_forum] MgO slab calculation: unexpected Fermi energy shift

[Dingfu Shao]

Hi, Yue-Wen,

You need to set occupations='fixed'  for insulator. 'Smearing' is for metal.

Best regards,

Ding-Fu




*Ding-Fu Shao, Ph. D.*


*Department of Physics and Astronomy, University of Nebraska-Lincoln*

*Lincoln, NE **68588-0299*

*Email: dingfu.shao at gmail.com <dingfu.shao at gmail.com>*

2016-04-22 4:43 GMT-05:00 Yue-Wen Fang <yuewen.fang at gmail.com>:

> Dear all,
>
> I calculated a MgO slab model with two* symmetrical* interface using 3
> different DFT codes using plane wave method. The other two shows this slab
> is an insulator, and the results are almost completely same.
>
> However, pwscf calculation show it is a metal with an unexpected Fermi
> shift in the density of states although the shape of DOS is similar to
> those obtained from other DFTcodes. I think this is caused my incorrect
> settings, but I haven't found what specific factor causes this error.
>
> The scf and nscf input files are shown in the last part, hopefully experts
> could give some suggestions. Many thanks.
>
> *PS:*
> Because it is just a test, I only used about 6 Angstrom in this model. I
> checked the potential in every DFT code, there is no slope of potential in
> vacuum, which indicates there is no unexpected artificial field is induced.
>
>
> *SCF calculation input:*
>
> &control
>  calculation = 'scf',
>  verbosity = 'high',
>  restart_mode = 'from_scratch',
>  prefix = 'mgo',
>  tstress = .false.,
>  tprnfor = .false.,
>  pseudo_dir = '.',
>  outdir = '.'
>  wf_collect=.true.
> /
> &system
>  ibrav=0, nat=6, ntyp=2,
>  ecutwfc=25,
>  ecutrho=300,
>  occupations='smearing',
>  smearing='gaussian',
>  degauss=0.001,
> /
> &electrons
>  diagonalization='david',
>  mixing_mode = 'plain',
>  mixing_beta = 0.7,
>  conv_thr =  1.0d-7,
> /
> ATOMIC_SPECIES
>  Mg 24.305000 Mg.pbe-nsp-bpaw.UPF
>  O 15.999400 O.pbe-van_ak.UPF
> ATOMIC_POSITIONS crystal
>  Mg 0.000000 0.000000 0.370955
>  Mg 0.500000 0.500000 0.500000
>  Mg 0.000000 0.000000 0.629045
>  O 0.500000 0.500000 0.370955
>  O 0.000000 0.000000 0.500000
>  O 0.500000 0.500000 0.629045
> K_POINTS {Automatic}
> 7 7 1 0 0 0
> CELL_PARAMETERS bohr
> 5.627166 0.000000 0.000000
> 0.000000 5.627166 0.000000
> 0.000000 0.000000 30.834283
>
>
> *NSCF calculation input:*
>
> &control
>  calculation = 'nscf',
>  verbosity = 'high',
>  restart_mode = 'from_scratch',
>  prefix = 'mgo',
>  tstress = .false.,
>  tprnfor = .false.,
>  pseudo_dir = '.',
>  outdir = '.'
>  wf_collect=.true.
> /
> &system
>  ibrav=0, nat=6, ntyp=2,
>  ecutwfc=25,
>  ecutrho=300,
>  occupations='tetrahedra',
> /
> &electrons
>  diagonalization='david',
>  mixing_mode = 'plain',
>  mixing_beta = 0.7,
>  conv_thr =  1.0d-7,
> /
> ATOMIC_SPECIES
>  Mg 24.305000 Mg.pbe-nsp-bpaw.UPF
>  O 15.999400 O.pbe-van_ak.UPF
> ATOMIC_POSITIONS crystal
>  Mg 0.000000 0.000000 0.370955
>  Mg 0.500000 0.500000 0.500000
>  Mg 0.000000 0.000000 0.629045
>  O 0.500000 0.500000 0.370955
>  O 0.000000 0.000000 0.500000
>  O 0.500000 0.500000 0.629045
> K_POINTS {Automatic}
> 11 11 2 0 0 0
> CELL_PARAMETERS bohr
> 5.627166 0.000000 0.000000
> 0.000000 5.627166 0.000000
> 0.000000 0.000000 30.834283
>
> --
>
> ------------------------------------------------------------------------------------------------------------
> Yue-Wen FANG, PhD student
> East China Normal University <http://english.ecnu.edu.cn/>, China
> Japan Fine Ceramics Center, Japan
>
>
>
>
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