[QE-users] (no subject)

[Guangyao Gao]

Dear QE community,


I have difficulty when calculating the band structure for Co3O4. I used the
conventional unit cell and optimized the structure. I performed a band
structure calculation and I got a small bandgap (about 0.6 eV). This makes
sense because Co3O4 is a semi-conductor. Then I performed a band structure
calculation with a Hubbard correction and expecting a bigger bandgap.
However, the band structure diagram looks very strange. The band was gone,
which means the valence band and conduction band are overlapping with each
other. I was expecting the band will be bigger because of the Hubbard
correction and I was surprised because I got the opposite result. Then I
tried to increase the Hubbard value by about 1 eV, the result stays the
same: no gaps. and the diagram for both Hubbard correction calculations
looks very similar.


As I mentioned, I really think the bandgap will be bigger with the Hubbard
correction, I believe there is something wrong with my calculation, but I
just don’t understand where I got wrong and I am not even sure why
the hubbard value is not acting on the metal. How can I explain this
phenomenon? Does anyone ever have this similar issue? Any insights about
how can I possibly figure this out?


Here is the main part of my input file.


Thank you so much!


&control

    calculation   = 'scf'

    restart_mode  = 'from_scratch'

    prefix        = ‘$’

    pseudo_dir    = '$$'

    outdir        = '$$$'

    nstep         = 200

    max_seconds   = 324000

    wf_collect    =.FALSE.

/

&system

    ibrav=1, celldm(1)=15.1884, nat=56, ntyp=2,

    ecutwfc=300.0,ecutrho=1200.0,

    occupations = 'smearing',degauss=0.010d0

    smearing = 'mp'

    nspin = 2

    starting_magnetization(1)= 0.1

    lda_plus_u=.TRUE.

    Hubbard_U(1)=5.9

/

&electrons

    conv_thr=1.0d-6, electron_maxstep=1000,

    mixing_mode='plain', mixing_beta=0.1,diagonalization='cg'

/

$ions

    ion_dynamics='bfgs'

/

&cell

    cell_dynamics='bfgs'

/

ATOMIC_SPECIES

  Co  58.933  Co_pbe_v1.2.uspp.F.UPF

  O   15.999  O_pbe_v1.2.uspp.F.UPF

  ATOMIC_POSITIONS crystal

Co            0.2499990992        0.2499990992        0.2499990992

***

***

***

O             0.1147028366        0.3852969334        0.1147028366


K_POINTS Automatic

4 4 4 0 0 0


Sincerely,


Yao
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