[Pw_forum] Improve convergence, slab and electric field.

[Tone Kokalj]

On Thu, 2010-09-02 at 08:38 -0500, joaquin peralta wrote:
> Thanks, i obtain more fast convergence for 1V/A, but ...
> 
> If I use the previous results from 1V/A in order to calculate an
> increase in the Field i obtain fluctuation in the energy.
> 
>      total energy              =    -261.46819272 Ry
>      total energy              =    -261.46815798 Ry
>      total energy              =    -261.46816720 Ry
>      total energy              =    -261.46260676 Ry
>      total energy              =    -261.37365516 Ry
>      total energy              =    -261.46820680 Ry
>      total energy              =    -261.46821935 Ry
>      total energy              =    -261.46807352 Ry
>      total energy              =    -261.46825528 Ry
>      total energy              =    -261.46820900 Ry
>      total energy              =    -261.46803348 Ry
> 
> for my case, is recommendable reduce the precision by default of the
> energy convergence from 1D-4 to 1D-3? 

To what energy threshold are you referring: conv_thr (in &electrons) or
etot_conv_thr (in &control). According to the value of 1d-3/1d-4 I would
assume the latter; note however that the latter has nothing to do with
the SCF convergence, as it is an optimization threshold criteria for
geometry optimizer.

If you use 1d-4 for the conv_thr, then the value is much too high, it
should be 1d-6 or, even better, lower than that.

After how many SCF cycles these "fluctuations" appear? 

You may try to reduce mixing_beta to 5%, ...

The following considerations will speed-up your calculations, hence you
will be able to do more SCF convergence tests: from the previous emails
of yours, I notice that you use over 50 Angs of vacuum, which is HUGE (I
would assume that about 25 Angs should be sufficient; in this case there
will be more than 10 Angs spacing from the slab to the dipole-layer). I
also noticed that ecutwfc/ecutrho of 30/500 ry is a very large number
for Aluminum. 

Regards, Tone
-- 
Anton Kokalj
J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia 
(tel: +386-1-477-3523 // fax:+386-1-477-3822)

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