[QE-users] Medium-entropy materials

[Connor Wilson]

Hi everyone,

I am trying to obtain a converged SCF calculation (using Quantum ESPRESSO, version 7.0) for the medium-entropy oxide (CoCuMgZn)0.25 O. This material crystalizes in the rocksalt structure. I am using a 64-atom supercell. I have attached my input file at the end of this message.

My problem is: after 50 iterations, my calculations show no trend towards convergence (ie. the 'estimated scf accuracies' in the pw.x output file stabilize around 0.5 Ry). I have made the following adjustments in an effort to achieve better convergence:

  *   using degauss values of 0.001, 0.01, 0.02
  *   using a 6 x 6 x 6 K-mesh
  *   using mixing_beta of 0.05, 0.1, 0.2
  *   using ecutwfc of 60, 70, 100 (each with 10x ecutrho)
  *   using PBEsol, PBE pseudopotentials

My question is: do you think it is possible to achieve a converged SCF calculation using QE? If it is, what might an appropriate value of conv_thr be, and could you suggest other changes to my input file I could try?

Thank you for your time,


Connor Wilson
Brock University
Department of Mathematics and Science
1812 Sir Issac Brock Way, St. Catharines, ON, CAN, L2S 3A1






######################## pw.x input ###########################

&CONTROL
  calculation = 'scf',
  prefix = 'MEO',
  tstress = .true.,
  tprnfor = .true.,
  restart_mode = 'from_scratch',
  outdir = '/home/cw279/projects/def-crandles/cw279/MEO/222c/alat'
  pseudo_dir = '/home/cw279/pseudo',
/

&SYSTEM
  ibrav = 1,
  celldm(1) = 15.1,
  nat = 64,
  ntyp = 5,
  ecutwfc = 100,
  ecutrho = 1000,
  occupations = 'smearing',
  smearing = 'mv',
  degauss = 0.01,
/

&ELECTRONS
  electron_maxstep = 50,
  mixing_beta = 0.1,
  conv_thr  = 1.0d-6,
  mixing_mode = 'local-TF',
  mixing_ndim = 10,
/

ATOMIC_SPECIES
  Mg  24.305   Mg.pbe-spnl-kjpaw_psl.1.0.0.UPF
  O   15.9994  O.pbe-n-kjpaw_psl.1.0.0.UPF
  Zn  65.380   Zn.pbe-dnl-kjpaw_psl.1.0.0.UPF
  Ni  58.6934  Ni.pbe-spn-kjpaw_psl.1.0.0.UPF
  Co  58.9332  Co.pbe-spn-kjpaw_psl.0.3.1.UPF

K_POINTS {automatic}
  4 4 4  0 0 0

ATOMIC_POSITIONS {crystal}
........

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