[QE-users] convergence NOT achieved

[Giuseppe Mattioli]

Dear Seyed Mehrdad Zamzamian
If you didn't try it yet, you may try to start from the structure  
obtained by performing a calculation with NC or PAW pseudopotentials.  
You can also (carefully) try to use this key

  &electrons
     scf_must_converge=.false.,
  /

It forces the geometry step even if the wavefunctions are not fully  
converged. It is a sensible choice when the scf steps dances slightly  
above convergence, or even to move away from problematic but not very  
wrong atomic positions.

HTH
Giuseppe

Quoting mehrdad zamzamian <mehrdad.zamzamian at gmail.com>:

> With regards
> Maybe my question is very repetitive but i could found nothing in the forum
> to help. I am trying to run a vc-relax for cementite structure using
> GGA-USPP. The problem is that i cannot achieve any convergence even after
> 1000 iteration. The total energy fluctuates in the order of ~0.1! By using
> other PP, i simply achieved to the convergence, but i need to use these pp
> ones. I would appreciate any suggestions in this regard.
> This is my input:
> &CONTROL
>     calculation   = "vc-relax"
>     forc_conv_thr =  1.00000e-03
>     max_seconds   =  8.64000e+07
>     nstep         = 1000
>     pseudo_dir    = "..../bin"
> /
>
> &SYSTEM
>     a                         =  5.03018e+00
>     angle1(1)                 =  0.00000e+00
>     angle2(1)                 =  0.00000e+00
>     b                         =  6.73931e+00
>     c                         =  4.49084e+00
>     degauss                   =  1.00000e-02
>     ecutrho                   =  6.37306e+02
>     ecutwfc                   =  7.08118e+01
>     ibrav                     = 8
>     lda_plus_u                = .FALSE.
>     nat                       = 16
>     nspin                     = 2
>     ntyp                      = 2
>     occupations               = "smearing"
>     smearing                  = "gaussian"
>     starting_magnetization(1) =  4.00000e-01
>     starting_magnetization(2) =  0.00000e+00
> /
>
> &ELECTRONS
>     conv_thr         =  1.00000e-06
>     electron_maxstep = 2000
>     mixing_beta      =  4.00000e-01
>     startingpot      = "atomic"
>     startingwfc      = "atomic+random"
> /
>
> &IONS
>     ion_dynamics = "bfgs"
> /
>
> &CELL
>     cell_dofree    = "xyz"
>     cell_dynamics  = "bfgs"
>     press          =  0.00000e+00
>     press_conv_thr =  5.00000e-01
> /
>
> K_POINTS {automatic}
>  2  2  3  0 0 0
>
> ATOMIC_SPECIES
> Fe     55.84500  Fe.pbe-spn-rrkjus_psl.1.0.0.UPF
> C      12.01070  C.pbe-n-rrkjus_psl.1.0.0.UPF
>
> ATOMIC_POSITIONS {angstrom}
> Fe      0.892203   0.460793   1.491414
> Fe      4.137977   6.278514   2.999431
> Fe      1.622887   6.278514   3.736836
> Fe      3.407293   0.460793   0.754008
> Fe      3.407293   2.908860   0.754008
> Fe      1.622887   3.830447   3.736836
> Fe      4.137977   3.830447   2.999431
> Fe      0.892203   2.908860   1.491414
> Fe      0.184411   1.684827   3.759376
> Fe      4.845769   5.054480   0.731469
> Fe      2.330679   5.054480   1.513954
> Fe      2.699502   1.684827   2.976891
> C       0.618742   5.054480   2.519058
> C       4.411438   1.684827   1.971786
> C       1.896348   1.684827   0.273636
> C       3.133833   5.054480   4.217209
>
> Thanks
>
> Seyed Mehrdad Zamzamian
> Sharif University of Technology, Tehran, Iran
> Energy engineering department
> E-mail: mehrdad.zamzamian at gmail.com



GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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E-mail: <giuseppe.mattioli at ism.cnr.it>