[Pw_forum] problem of convergence

[Cyrille Barreteau]

Dear pwscf users and developpers,

I am trying to do a pwscf calculation of a 100 iron surface.
I first performed a scf calculation on a 11 layers thick
slab without any difficulty. But to get a better description
of the surface I have tried to perform a calculation with
a thicker slab: 20 atomic layers. Then comes the difficulty:
the scf cycle never converges. After 46 iterations the
estimated scf accuracy is huge (see below).
Any hint to improve convergency?
  -decreasing mixing?
  -changing occupation
  -changing degauss...

  thank you in advance
     Cyrille

====================================================
     iteration # 46     ecut=    35.00 ryd     beta=0.30
     Davidson diagonalization with overlap
     ethr =  2.46E-03,  avg # of iterations =  6.7

     total cpu time spent up to now is 228848.87 secs

     total energy              = -1200.62214988 ryd
     estimated scf accuracy    <  4756.34124938 ryd

     total magnetization       =    10.95 Bohr mag/cell
     absolute magnetization    =    11.56 Bohr mag/cell
=====================================================

Here is the input file:

==============================================
 &control
    calculation='scf'
    title='Fe 001 20 layers +   vacuum'
    restart_mode='from_scratch',
    prefix='fe_surf_001_gga'
    pseudo_dir = '/home/barreto/SOFTWARE/pseudo/',
    outdir='tmp'
 /
 &system
    ibrav = 6, celldm(1) = 5.42351511431617127800 , celldm(3)=13,
     nat= 20, ntyp= 1,nbnd=150,nspin=2,
    ecutwfc = 35.0, ecutrho=250.,starting_magnetization(1)=0.3,
    occupations='smearing', smearing='methfessel-paxton', degauss=0.025
 /
 &electrons
    conv_thr =  1.0d-8
    mixing_beta = 0.3
 /
ATOMIC_SPECIES
 Fe 55.847 Fe_us_gga_d2.1.8.pseudo.UPF
ATOMIC_POSITIONS
Fe   0.000000000000000  0.000000000000000   -5.25000000000000
Fe   0.500000000000000  0.500000000000000   -4.75000000000000
Fe   0.000000000000000  0.000000000000000   -4.25000000000000
Fe   0.500000000000000  0.500000000000000   -3.75000000000000
Fe   0.000000000000000  0.000000000000000   -3.25000000000000
Fe   0.500000000000000  0.500000000000000   -2.75000000000000
Fe   0.000000000000000  0.000000000000000   -2.25000000000000
Fe   0.500000000000000  0.500000000000000   -1.75000000000000
Fe   0.000000000000000  0.000000000000000   -1.25000000000000
Fe   0.500000000000000  0.500000000000000   -0.75000000000000
Fe   0.000000000000000  0.000000000000000   -0.25000000000000
Fe   0.000000000000000  0.000000000000000    0.25000000000000
Fe   0.500000000000000  0.500000000000000    0.75000000000000
Fe   0.000000000000000  0.000000000000000    1.25000000000000
Fe   0.500000000000000  0.500000000000000    1.75000000000000
Fe   0.000000000000000  0.000000000000000    2.25000000000000
Fe   0.500000000000000  0.500000000000000    2.75000000000000
Fe   0.000000000000000  0.000000000000000    3.25000000000000
Fe   0.500000000000000  0.500000000000000    3.75000000000000
Fe   0.000000000000000  0.000000000000000    4.25000000000000
Fe   0.500000000000000  0.500000000000000    4.75000000000000
Fe   0.000000000000000  0.000000000000000    5.25000000000000
K_POINTS automatic
 14 14 1 0 0 0
==========================================================








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Cyrille Barreteau  | phone : +33 (0)1 69 08 29 51
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