[QE-users] Question about BaO rocksalt structure calculation

[Wente Li]

Dear all Quantum espresso users

I am a new person to quantum espresso. Recently, I am doing some simple
bulk calculations for some rocksalt oxide. I focus on BaO. Obviously, it is
a fcc cell. In a conventional cell, it has 8 atoms in tootal. Or, we can
rotate it 45 degree and a tetragonal cell. Or in the primitive cell, we
have one Ba and one O.

For tetragonal cell, I always meet convergence issue because estimated scf
accuracy is larger then 10000 ry. Although in the end, it converges in a
scf step, however, the eigenvalues are strange:
        k = 0.0000-0.5000 0.0000 (  4674 PWs)   bands (ev):

  ************************************************************************
  ******************************************************-977.8829-977.8797
  -911.8948-911.8928-907.9337-907.9317
The reason for so many stars is the value is too large. The total energy is
-7429.48 ry.

Here is my input file:
&control
    calculation = 'vc-relax'
    restart_mode='from_scratch'
    prefix = 'bao'
    outdir = './outdir'
    pseudo_dir = './'
/
&system
    ibrav=0
    nat=4, ntyp=2,
    ecutwfc=60
    ecutrho=600
    occupations='tetrahedra'
/
&electrons
    conv_thr=1e-6
/
&ions
    ion_dynamics = 'bfgs'
/
&cell
     cell_dynamics = 'bfgs'
/

ATOMIC_SPECIES
 O  15.999  O.pz-n-kjpaw_psl.0.1.UPF
 Ba 24.305  Ba.pz-spn-kjpaw_psl.1.0.0.UPF

ATOMIC_POSITIONS (crystal)
 Ba   0.00 0.00 0.00
 Ba   0.50 0.50 0.50
 O    0.50 0.50 0.00
 O    0.00 0.00 0.50

K_POINTS (automatic)
  4 4 4 0 0 0

CELL_PARAMETERS { bohr }
   7.502212717  0.0000000  0.0000000
   0.0000000    7.5022127170  0.0000000
   0.0000000  0.0000000   10.609730971809

Right Here, I use LDA-PAW PP. If I use PBE-PAW, convergence is
better. However, if I make a supercell of 10 unit cells, it does not
converge. Cubic conventional cell also does not converge. However, if I use
a primitive cell, there is no problem.

I tried another oxide, MgO with tetragonal, cubic conventional and
primitive cell, everything is fine.

Thank you all for your help.

Best,
W. Li
Department of Physics, UT Austin
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20200707/717c0716/attachment.html>