[Pw_forum] vc-relax of R-3c structure does not converge

[lung Fermin]

Dear QE community,

I want to calculate the phonon diseprsion relation of PbTiO3 in the
strucutre of R-3c spacegroup. First I did the vc-relax using the
experimental lattice parameters. However, the scf calculation fails to
converge within 100 iteration and the job exits with error. I have tried
changing the mixing_beta to 0.3 and mixing_ndim to 10, but still fails. I
am a newbie to QE. May someone please give me some advices on this issue?

INPUT file:
 &control
    calculation='vc-relax',
    restart_mode='from_scratch',
    prefix='PbTiO3',
    outdir = './tmp/',
    pseudo_dir = '$PSD_DIR',
    max_seconds = 4.1D+6
 /
 &system
    nat = 10
    ntyp = 3
    ibrav = 5
    celldm(1) = 10.037,
    celldm(4) = 0.53,
    ecutwfc =60
 /
 &electrons
   mixing_beta=0.3D0,
   mixing_ndim=10
 /
 &ions
 /
&cell
 /
ATOMIC_SPECIES
Pb  207.2  Pb.pbe-spn-rrkjus_psl.1.0.0.UPF
Ti  47.867  Ti.pbe-spn-rrkjus_psl.1.0.0.UPF
O  15.999  O.pbe-n-rrkjus_psl.1.0.0.UPF
ATOMIC_POSITIONS {alat}
Pb  0.25 0.25 0.25
Pb  0.75 0.75 0.75
Ti  0.00 0.00 0.00
Ti  0.50 0.50 0.50
O  0.62351014  0.87648986
0.25000000
O  0.37648986  0.12351014  0.75000000
O  0.87648986  0.25000000  0.62351014
O  0.12351014  0.75000000  0.37648986
O  0.25000000  0.62351014  0.87648986
O  0.75000000  0.37648986  0.12351014
K_POINTS AUTOMATIC
15 15 15 0 0 0

Thanks in advance.
Fermin
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