[Pw_forum] Total energy does not converge with respect to ecut variation

[Seyed Mojtaba Rezaei Sani]

Dear all

I was performing an optimizing calculation for the kinetic energy cutoff of
 wavefunctions expansion for Cu3N compound with a cubic structure using
QE v.5.1.
Results don't show any convergence neither in total energies nor in
differences.
Here is the table for the calculation result

25.out:!    total energy              =    -224.54499924 Ry
30.out:!    total energy              =    -231.56190061 Ry
35.out:!    total energy              =    -239.33860506 Ry
40.out:!    total energy              =    -247.75926085 Ry
45.out:!    total energy              =    -256.35103303 Ry
50.out:!    total energy              =    -264.81580643 Ry
55.out:!    total energy              =    -272.59279950 Ry
60.out:!    total energy              =    -279.38896704 Ry

I chose these PPs:

Cu.pbe-d-hgh.UPF
N.pbe-hgh.UPF

and this an input file:

&CONTROL
  calculation = 'scf'
  verbosity = 'high'
  restart_mode = 'from_scratch'
  wf_collect = .TRUE.
  nstep =  100
  tstress = .TRUE.
  tprnfor = .TRUE.
  outdir = './tmp'
  prefix = 'Cu3N'
  etot_conv_thr = 0.0001
  forc_conv_thr = 0.0001
  pseudo_dir = '/home/rezaei/work/cu_pnictide/pseudo'
/
&SYSTEM
  ibrav = 1
  celldm(1) = 7.217
  nat = 4
  ntyp = 2
  ecutwfc = 25
  ecutrho = 100.0
  occupations = 'smearing'
  degauss = 0.02D0
  smearing = 'mv'
/
&ELECTRONS
  electron_maxstep = 100
  conv_thr = 1.0d-6
  mixing_mode = 'TF'
  mixing_beta = 0.7D0
  diagonalization = 'cg'
/
ATOMIC_SPECIES
  Cu   63.5460  Cu.pbe-d-hgh.UPF
  N    14.0067  N.pbe-hgh.UPF
ATOMIC_POSITIONS {alat}
  N        0.000000000   0.000000000   0.000000000
  Cu       0.000000000   0.500000000   0.000000000
  Cu       0.500000000   0.000000000   0.000000000
  Cu       0.000000000   0.000000000   0.500000000
K_POINTS {automatic}
  10 10 10  1 1 1

I appreciate any help in advance.

 Best regards,

-- 
Seyed Mojtaba Rezaei Sani

Institute for Research in Fundamental Sciences (IPM)
School of Nano-Science
Shahid Farbin Alley
Shahid Lavasani st
P.O. Box 19395-5531
Tehran, Iran
Tel: +98 21 2310  (3069)
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