[QE-users] No SCF convergence for simple actinide compounds

[Sergei Butorin]

Dear Lorenzo,

I have rather meant a simple structure and a small number of atoms of these compounds.

Yes, I did try the occupations=’smearing’ option, before posting a question, but only for a supercell. Probably, I used too small degauss value. I also tried a larger number of k-points.

Anyhow, when I switched to DFT+U, things became somewhat better.

Best,
Sergei Butorin

From: users [mailto:users-bounces at lists.quantum-espresso.org] On Behalf Of Lorenzo Paulatto
Sent: Friday, 31 July 2020 16:39
To: Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org>
Subject: Re: [QE-users] No SCF convergence for simple actinide compounds

I wouldn't call an oxide of Plutonium "simple"... My guess is that it becomes metallic in simple DFT, try to treat it as such, by setting occupations="smearing"

Cheers
--
Lorenzo Paulatto

On Thu, 30 Jul 2020, 18:44 Sergei Butorin, <sergei.butorin at physics.uu.se<mailto:sergei.butorin at physics.uu.se>> wrote:
I use QE 6.4.1 and have encountered a problem of pure or no-convergence in scf runs for simple actinide compounds. For example, for PuO2, I get quick convergence for a primitive cell but for a conventional unit cell the convergence to ‘poor’ conv_thr=1.1d-6 is reached only after 560 iterations with the same parameters and pseudos in the input file (see below):

&control
  calculation = 'scf'
  verbosity='high'
  prefix = 'system'
  pseudo_dir = '/My_input/PuO2/'
  outdir = './Out'
  wfcdir = 'undefined'
  tstress = .false.
  tprnfor = .false.
/
&system
    ibrav = 0
  A =    5.39819
    nat   = 12
    ntyp  = 2
  noncolin = .false.
  lspinorb = .false.
  ecutwfc = 50
  ecutrho = 400
  occupations = 'fixed'
  nspin  = 1
/
&electrons
  conv_thr = 1.1d-6
  mixing_beta = 0.3
  electron_maxstep = 2000
  startingwfc = 'atomic+random'
  diagonalization = 'david'
/
&ions
/
ATOMIC_SPECIES
Pu   239.0522      Pu.pbe-spfn-rrkjus_psl.1.0.0.UPF
O   15.9994        O.pbe-n-rrkjus_psl.1.0.0.UPF
CELL_PARAMETERS alat
  1.000000000000000   0.000000000000000   0.000000000000000
  0.000000000000000   1.000000000000000   0.000000000000000
  0.000000000000000   0.000000000000000   1.000000000000000
ATOMIC_POSITIONS crystal
Pu   0.000000000000000   0.000000000000000   0.000000000000000
Pu   0.000000000000000   0.500000000000000   0.500000000000000
Pu   0.500000000000000   0.000000000000000   0.500000000000000
Pu   0.500000000000000   0.500000000000000   0.000000000000000
 O   0.250000000000000   0.250000000000000   0.250000000000000
 O   0.750000000000000   0.250000000000000   0.750000000000000
 O   0.750000000000000   0.750000000000000   0.750000000000000
 O   0.250000000000000   0.750000000000000   0.750000000000000
 O   0.250000000000000   0.250000000000000   0.750000000000000
 O   0.750000000000000   0.250000000000000   0.250000000000000
 O   0.250000000000000   0.750000000000000   0.250000000000000
 O   0.750000000000000   0.750000000000000   0.250000000000000
K_POINTS automatic
2  2  2  1  1  1

Things I have tried to improve the situation but without success:

1. Significantly increasing ecutwfc and ecutrho values and keeping the 10-12 ratio for US pseudos.
2. Using NC pseudos both from the sg15 collection and harder TM pseudos with smaller rc with appropriate ecutwfc and ecutrho values in my pw.x input.
3. Smaller mixing-beta down to 0.1.
4. Different mixing_mode (e.g. 'local-TF').
5. Different diagonalization ('cg').

No wonder that in case of a supercell, the convergence value goes only down to a few Ry at best. The occupations = 'smearing' option does not help either.

Similar problems I have encoutered for UO2, although I have not investigated that case in detail.

My question is whether QE (pw.x) is generally so bad in handling the f-element systems or something is really wrong on my side.

Dr. Sergei Butorin
Uppsala University
Sweden








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