[QE-users] convergence NOT achieved using DFT+U

[Antonio Pancho Ramirez]

Dear Members,

I have been working with LiCoO2 and CoO2, performing DFT calculation to determine  the intercalation potential. However,  when it comes to CoO2 after adding  the Hubbard correction (DFT+U) convergences cannot  be reached. I have just added two lines to the original input file: lda_plus_u = .true. and Hubbard_U(1) = 3.4 (this value I took from a paper: Aykol, M., Kim, S., & Wolverton, C. (2015). Van der Waals interactions in layered lithium cobalt oxides. The Journal of Physical Chemistry C, 119(33), 19053-19058.). I have performed all the calculations using QE v.6.7MaX.

Kindly have a look at the input file and suggest why its so hard to converge this relatively simple system after adding the U correction

&CONTROL
  calculation = 'scf'
  outdir='tmp',
  prefix = 'CoO_U'
  pseudo_dir = '.',
  tprnfor = .true.
  verbosity = 'high'
/
&SYSTEM
  ecutrho = 800
  ecutwfc = 70
  ibrav = 0
  nat = 3
  ntyp = 2
  occupations='smearing', smearing='gauss', degauss=0.015,
  nspin=2
  starting_magnetization(1) = 0.1
  lda_plus_u = .true.,
  Hubbard_U(1) = 3.4
  vdw_corr='grimme-d3'

/
&ELECTRONS
/
ATOMIC_SPECIES
Co  58.933194 co_pbe_v1.2.uspp.F.UPF
O   15.999    o_pbe_v1.2.uspp.F.UPF
CELL_PARAMETERS angstrom
      2.8413505554       0.0000000000       0.0000000000
      1.4206751885       2.4606823642       0.0000000000
      1.4206754552       0.8202267469       4.7143528794
ATOMIC_POSITIONS crystal
Co           0.0000000000       0.0000000000       0.0000000000
O            0.7396634820       0.7396634820       0.7810095550
O            0.2603365180       0.2603365180       0.2189904750
K_POINTS automatic
6 6 6 0 0 0

I had already tried to change the conv_thr, diagonalization, etc.  as it is show below

  conv_thr        =  1e-5
   diagonalization =  'cg'
   mixing_beta     =  0.3
   mixing_mode     =  'local-TF'

But noting seems to work. I believe that the problem could be related to the magnetization (hing and low spin state). Maybe to force the system to low spin state but I not sure how to do that or if the problem is connected with that. Additionally, I use gbrv pseudopotential for these calculation.


Best regards

William Pancho

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