[Pw_forum] MgO slab calculation: unexpected Fermi energy shift

[Yue-Wen Fang]

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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