[QE-users] Advices on ralaxing perovskite supercells

[Luiz Gustavo Davanse da Silveira]

Greetings,

I am using QE 6.4.1 to relax the atomic positions of a BiFeO3 40 atom
supercell, but the calculation didn't converge after 100 scf steps (the
final scf accuracy was about 5E-4). I am a new QE user and I really don't
know what to change in order to the calculation successfully run. Any
advice is very much appreciated.

My input follows bellow:

&control
	calculation = 'relax'
	prefix = 'bfo'
	pseudo_dir = './sssp'
	outdir = './outdir'
	etot_conv_thr = 1.0e-5
	forc_conv_thr = 1.0e-4
/
&system
	ibrav = 0
	nat = 40, ntyp = 3,
	ecutwfc = 120, ecutrho = 960
	lda_plus_u = .TRUE., Hubbard_U(2) = 4
/
&electrons
	conv_thr = 1e-6
/
&ions
	ion_dynamics = 'bfgs'
/
ATOMIC_SPECIES
 Bi 208.98 Bi_pbe_v1.uspp.F.UPF
 Fe 55.85 Fe.pbe-spn-kjpaw_psl.0.2.1.UPF
 O 16 O.pbe-n-kjpaw_psl.0.1.UPF
ATOMIC_POSITIONS (crystal)
 Bi 0.000000000000000     0.000000000000000     0.000000000000000
 Bi 0.500000000000000     0.000000000000000     0.000000000000000
 Bi 0.000000000000000     0.500000000000000     0.000000000000000
 Bi 0.500000000000000     0.500000000000000     0.000000000000000
 Bi 0.000000000000000     0.000000000000000     0.500000000000000
 Bi 0.500000000000000     0.000000000000000     0.500000000000000
 Bi 0.000000000000000     0.500000000000000     0.500000000000000
 Bi 0.500000000000000     0.500000000000000     0.500000000000000
 Fe 0.250000000000000     0.250000000000000     0.250000000000000
 Fe 0.750000000000000     0.250000000000000     0.250000000000000
 Fe 0.250000000000000     0.750000000000000     0.250000000000000
 Fe 0.750000000000000     0.750000000000000     0.250000000000000
 Fe 0.250000000000000     0.250000000000000     0.750000000000000
 Fe 0.750000000000000     0.250000000000000     0.750000000000000
 Fe 0.250000000000000     0.750000000000000     0.750000000000000
 Fe 0.750000000000000     0.750000000000000     0.750000000000000
 O  0.187667999289205     0.312332000710795     0.000000000000000
 O  0.812332000710795     0.187667999289205     0.000000000000000
 O  0.312332000710795     0.687667999289205     0.000000000000000
 O  0.687667999289205     0.812332000710795     0.000000000000000
 O  0.312332000710795     0.187667999289205     0.500000000000000
 O  0.687667999289205     0.312332000710795     0.500000000000000
 O  0.187667999289205     0.812332000710795     0.500000000000000
 O  0.812332000710795     0.687667999289205     0.500000000000000
 O  0.000000000000000     0.187667999289205     0.312332000710795
 O  0.500000000000000     0.312332000710795     0.187667999289205
 O  0.000000000000000     0.812332000710795     0.187667999289205
 O  0.500000000000000     0.687667999289205     0.312332000710795
 O  0.000000000000000     0.312332000710795     0.687667999289205
 O  0.500000000000000     0.187667999289205     0.812332000710795
 O  0.000000000000000     0.687667999289205     0.812332000710795
 O  0.500000000000000     0.812332000710795     0.687667999289205
 O  0.312332000710795     0.000000000000000     0.187667999289205
 O  0.687667999289205     0.000000000000000     0.312332000710795
 O  0.187667999289205     0.500000000000000     0.312332000710795
 O  0.812332000710795     0.500000000000000     0.187667999289205
 O  0.187667999289205     0.000000000000000     0.812332000710795
 O  0.812332000710795     0.000000000000000     0.687667999289205
 O  0.312332000710795     0.500000000000000     0.687667999289205
 O  0.687667999289205     0.500000000000000     0.812332000710795
K_POINTS (automatic)
 4 4 4 0 0 0
CELL_PARAMETERS (angstrom)
 7.8 0.0 0.0
 0.0 7.8 0.0
 0.0 0.0 7.8

Best regards,
Luiz G. D. Silveira
Universidade Federal do Paraná - Brazil