[Pw_forum] Convergence Problem

[Prasenjit Ghosh]

Hi Yang,

Here are a few general suggestions:

(1) Check the convergence wrt to vacuum (distance between periodic images).
In ur case it seems too small to me, as a result of which the periodic
images are interacting. I think this is specially important for ur case
because ur having an external electric field.

(2) check convergence wrt ecutrho & ecutwfc. Ususally ecutrho is 10-12 times
ecutwfc. (probably ur wave fn is not converged)

(3) a value of mixing beta=0.05 is too low. Such a low value often implies
that you don't move the electrons at all......hence its not very
effective........according to my experience,  at least for cal. without
electric field, a value of 0.2-0.3 works well.

(4) Also you are doing a slab cal. and usually either a few layers at the
bottom or a few in the middle are kept fixed (although this should not
affect ur electronic minimization).

With regards,
Prasenjit.



(5) ur value of conv_thr seem too high.....at least u should use the default
value. But I would suggest u to use something of the order of 10^-8.

2009/4/16 孙阳 <sunyang198498 at gmail.com>

> Thanks for your advice, Deng.
>
> Yang
>
> 2009/4/15 潘登 <panda.deng.pan at gmail.com>:
> > maybe the ecutwfc value is small.
> >
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