[QE-users] Wrong Fermi level with smearing compared to tetrahedra

Sat, 27 Jun 2020 05:55:39 -0700

Dear QE users,


I tried to search a solution for this problem and looked to the previous posts but didn't work with me



I made scf calculation for bulk SnS2 with dft-d3 using occupations= 'tetrahedra' I get the the fermi level Ef on top of the valence band as reported in the literature,

but when I try to use smearing the Ef will shifts about 1 eV to locate in the middle of the gap

I tried gaussian smearing and fd using a huge k points, but eventhough the energy converges to the value in tertahedra case, the Ef always shifts by ~ 1eV.

The only exception is mv smearing with 0.01 degauss it gives the right Ef, (but it has a tail with finite dos which is not seen in the gaussian case with wrong Ef, pls see the attached image) and when I try mv with 0.005 degauss it also show wrong Ef even with huge k points.


Does anyone know why I'm getting this shift in Ef even though the energy is converged and the kpoint is large enough


Here is the input file for tetrahedra and smearing:



Tetrahedra:


&control
    calculation = 'scf'
    restart_mode='from_scratch'
    prefix = 'tet'
    outdir = '/home/outdir'
    pseudo_dir = '/home/pseudo'
    verbosity = 'high'
/  

&system
  
    ibrav = 0,
    nat   = 6,
    ntyp  = 2,
    ecutwfc=80
    ecutrho=560
    vdw_corr = 'dft-d3'
    occupations='tetrahedra'
    nbnd=52
    lda_plus_u=.true.
    Hubbard_U(1)=9.0,
    Hubbard_U(2)=9.0,

/

&electrons
    conv_thr=1e-6
/

ATOMIC_SPECIES
 Sn    118.71000  Sn.pbe-dn-kjpaw_psl.1.0.0.UPF
 S      32.06600  S.pbe-n-kjpaw_psl.1.0.0.UPF

ATOMIC_POSITIONS (angstrom)

Sn      -0.000001900   2.129228760   7.368473930
Sn       1.843967305   1.064612836   1.474204489
S        1.843967305   1.064612836   8.846101191
S       -0.000001900   2.129228760   2.951831855
S       -0.000000000  -0.000000000  -0.005322640
S       -0.000000000   0.000000000   5.888946695

CELL_PARAMETERS (angstrom)

 3.687930810   0.000000000  -0.000000000
-1.843965405   3.193841769  -0.000000000
-0.000000000  -0.000000000  11.788538670
K_POINTS (automatic)
 20 20 6 0 0 0



Smearing



&control
    calculation = 'scf'
    restart_mode='from_scratch'
    prefix = 'smea'
    outdir = '/home/outdir'
    pseudo_dir = '/home/pseudo'
    verbosity = 'high'
/  

&system
  
    ibrav = 0,
    nat   = 6,
    ntyp  = 2,
    ecutwfc=80
    ecutrho=560
    vdw_corr = 'dft-d3'
    occupations='smearing',smearing='gaussian',degauss=0.01
    lda_plus_u=.true.
    Hubbard_U(1)=9.0,
    Hubbard_U(2)=9.0,
/

&electrons
    conv_thr=1e-6
/

ATOMIC_SPECIES
 Sn    118.71000  Sn.pbe-dn-kjpaw_psl.1.0.0.UPF
 S      32.06600  S.pbe-n-kjpaw_psl.1.0.0.UPF

ATOMIC_POSITIONS (angstrom)

Sn      -0.000001900   2.129228760   7.368473930
Sn       1.843967305   1.064612836   1.474204489
S        1.843967305   1.064612836   8.846101191
S       -0.000001900   2.129228760   2.951831855
S       -0.000000000  -0.000000000  -0.005322640
S       -0.000000000   0.000000000   5.888946695

CELL_PARAMETERS (angstrom)

 3.687930810   0.000000000  -0.000000000
-1.843965405   3.193841769  -0.000000000
-0.000000000  -0.000000000  11.788538670
K_POINTS (automatic)
 32 32 10 0 0 0


Houcine BOUZID
Sungkyunkwan University,

 

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