[Pw_forum] Convergence Problem

[Gabriele Sclauzero]

On top of what alreay said by the other users, I would suggest few more things:
> Below is the input file. Any suggestion is highly appreciated.
> 
> 
> 
> 
> &control
>     calculation='scf'
>     restart_mode='from_scratch',
>     pseudo_dir = '$PSEUDO_DIR/',
>     outdir='$TMP_DIR/'
>     prefix='Pd'
>     tefield = .true.
>     dipfield = .true.
>     nstep = 300
> 
>  /
>  &system
>     ibrav = 6
>     celldm(1) = 7.3331
>     nspin = 2
>     celldm(3) = 4.5
>     edir = 3
>     emaxpos=0.72
>     eopreg=0.28
>     eamp = -0.001944

I don't know much about efield calculations, but I suppose that you are sure that you 
placed the discontinuity of the potential in the vacuum, as should be done.

>     starting_magnetization=0.05

To be rigorous, starting_magnetization is a vector. In order to avoid strange surprises, 
you should specify
    starting_magnetization(1)=0.05
    ...

>     ntyp = 1
>     nat= 14
>     ecutwfc = 25.0,
>     ecutrho = 500.0,
>     occupations='smearing',
>     degauss=0.2

This value of degauss (which is in Ryd, NOT eV) seems exceedingly high to me. I would use 
something like at least 1 order of magnitude smaller (but you should test convergence by 
yourself, together with the k-point mesh).

You may also want to try different kind of smearing methods. Methfessel-Paxton usually 
works well with metals (smearing="mp")

>     nbnd=160

Usually there is no need to specify the number of bands when using smearing. The number of 
bands which will be computed is automatically increased by the program to a safe choice.

>  /
> 
>  &electrons
>     conv_thr = 1.0e-4

See Ghosh's reply...

>     mixing_mode='local-TF'

have you tried a different mixing mode? I don't know if this is well suited for slab 
calculations.


HTH

GS

>     mixing_beta = 0.05
>     mixing_ndim = 12
> 
>  /
> ATOMIC_SPECIES
>  Pd  100  Pd.pz-nd-rrkjus.UPF
> ATOMIC_POSITIONS
> Pd       0.500000000   0.000000000  -1.496126804
> Pd       0.000000000   0.500000000  -1.496126804
> Pd       0.000000000   0.000000000  -1.002542052
> Pd       0.500000000   0.500000000  -1.002542051
> Pd       0.500000000   0.000000000  -0.501470158
> Pd       0.000000000   0.500000000  -0.501470158
> Pd       0.000000000   0.000000000   0.000000000
> Pd       0.500000000   0.500000000   0.000000000
> Pd       0.500000000   0.000000000   0.501470158
> Pd       0.000000000   0.500000000   0.501470158
> Pd       0.000000000   0.000000000   1.002542052
> Pd       0.500000000   0.500000000   1.002542051
> Pd       0.500000000   0.000000000   1.496126804
> Pd       0.000000000   0.500000000   1.496126804
> 
> 
> 
> 
> K_POINTS (automatic)
>  8 8 1 0 0 0
> 
> 
> 

-- 


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| Gabriele Sclauzero, PhD Student                  |
| c/o:   SISSA & CNR-INFM Democritos,              |
|        via Beirut 2-4, 34014 Trieste (Italy)     |
| email: sclauzer at sissa.it                         |
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