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

[Iurii TIMROV]

Dear William,


Do not forget to indicate your affiliation when posting on this forum.


> Hubbard_U(1) = 3.4 (this value I took from a paper: Aykol, M., Kim, S., & Wolverton, C. (2015).


This is not correct. They used VASP which uses different Hubbard projectors, while you are using QE with "atomic" Hubbard projectors. Check this paper: https://aip.scitation.org/doi/10.1063/1.4945608


I recommend to compute U using the HP code of QE. Also use 'ortho-atomic' instead of 'atomic' projectors, because the former are more accurate: http://theossrv1.epfl.ch/Main/DFTHubbard


> conv_thr        =  1e-5


This is too large. You should use 1e-10 -- 1e-15


> diagonalization =  'cg'


Better use "davidson"


How did you obtain your structure? Did you visualize it and check that all is correct? In the past I also modeled CoO2 and it converged fine (my input looks different from yours). Check available crystal structure databases and search for CoO2 there.


HTH


Iurii


--
Dr. Iurii TIMROV
Senior Research Scientist
Theory and Simulation of Materials (THEOS)
Swiss Federal Institute of Technology Lausanne (EPFL)
CH-1015 Lausanne, Switzerland
+41 21 69 34 881
http://people.epfl.ch/265334
________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of Antonio Pancho Ramirez <antoniopr1994 at hotmail.com>
Sent: Monday, February 14, 2022 10:27:42 AM
To: users at lists.quantum-espresso.org
Subject: [QE-users] convergence NOT achieved using DFT+U

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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